Adepta Sororitas: Unfortunately, not really a real army at this point. There are rumblings of a new book, but there have been for years and GW has neglected Sisters to the point that they’re Direct-Only and *very* expensive, with their whole army being very old pewter, now Finecast sculpts. They can pack a hell of a lot of Meltas and Flamers into an army, and they can make a reasonable Allied Detachment as one or two of their units such as Dominion Squads are still very strong, but as a pure force they are terribly lacking. The most expensive army to buy, hands-down.
Astra Militarum: Formerly known as the Imperial Guard, the human armies of the Imperium are characterised by their list-building options; you can bring a truly vast horde of infantry, a battalion of tanks, a rapid response force of air cavalry, or bring down the sky with a huge number of artillery guns. Once ‘locked in’ to a certain build, they tend to lack on-board flexibility, and they tend to be one of the less mobile armies, but they can command a huge amount of firepower, are very resilient through sheer weight of numbers or very heavily-armoured tanks, and can reach across the board with impunity. Shooting is their forte, but a enough Guardsmen fixing bayonets with a few well-chosen characters to help them out can deal a surprising amount of damage and soak up a lot of fire. They’re an expensive force, as the amount of Guardsmen or transports you’ll need is quite large, but they do get a fair selection of boxed deals to help out and their tanks can get quite expensive with upgrades which can mitigate the high price of the infantry swarms.
Blood Angels: A more mobile, faster variant of Space Marines with a focus on assault over the shooting-centric, more flexible Space Marines. With fairly cheap buff characters to reach high Weapon Skill, Initiative and Attacks values combined with army-wide Furious Charge to hit very hard when they charge, Blood Angels will attack first and attack hard. A high number of Melta weapons allows them to kill tanks once they get in close, and their anti-infantry power in combat is unparalleled with the feared Death Company, but they can have issues with killing enemy combat units even more powerful than they are or high-toughness monsters outside of firing a lot of Meltaguns at them. They end up being a similar price to Space Marines, with some lovely plastic kits, but can edge up as they utilise a lot of Jump Pack troops which come in 5-man boxes - however, overall, they work out cheaper than buying regular Space Marines plus a Transport, which is common for Space Marine special units.
Chaos Space Marines-- Chaos Space Marines tend towards fast melee units backed up by powerful anti-infantry firepower. One of the premier books for killing Space Marines, with a large number of AP3, often Ignores Cover weapons, and various specific anti-Space Marine advantages such as Preferred Enemy or Hatred. They also have very strong HQ options, which can be a big appeal to someone who likes their heroes (or rather, anti-heroes) to be real monsters in combat. They are also a fair bit cheaper than their Loyalist brethren and benefit from larger squad sizes as well as an in-Codex horde choice in Cultists, meaning that you can really flood the field with more Marine bodies than many people are used to. Their downsides tend to be Leadership and long-ranged, anti-tank shooting; while Meltaguns will do a spectacular job up close, and Autocannons are fairly common, Chaos can often struggle to deal with heavily armoured tanks or vehicles in cover. They also have higher Leadership than the Loyalist counterparts, but at the cost of losing And They Shall Know No Fear. As a result, you often have to be wary of being run down in combat or losing valuable firepower while your troops rally. Models-wise, Chaos are probably the most diverse range of miniatures: they get their own, rather nice range of models, plus the whole range of Space Marines ready for you to subvert to the whims of the Dark Gods. They can end up on the pricey side if you want a horde of models, but they average out in the middle of the pack in terms of price; especially so as they’re in the starter set.
Chaos Daemons: Chaos Daemons are a very random army that only plays by the rules in the technical sense. They can bring a lot of psychic powers, summoning more units from beyond the veil, and they can pull some crazy tricks with their gimmicks and non-summoning psychic powers; the infamous Screamerstar and Flying Circus are both Daemon builds - the former being a unit of nigh-invincible giant daemonic lampreys, and the latter being a sky full of very large, very strong Greater Daemons and Daemon Princes. They are a *very* random army, with their wargear selections being mostly randomised and a random chart to roll on in every shooting phase, which can lead to a very dice-dependant playstyle. Mitigating this, and the various synergies and combos needed to make units perform at their most efficient as well as the rather 'screw the rules, we play our own way' nature of a lot of their successful builds means Daemons are not particularly forgiving on new players. They’re a very expensive army as a lot of their units come in small box sizes; the Greater Daemons are also in desperate need of a re-sculpt. They do get a rather lovely multi-use plastic Daemon Prince kit ripe for conversions for a reasonable price, however; and even a few of them will push up your collection’s points value significantly. They’re an interesting army to paint, with at least four distinct styles and colours to use which can offset the ennui many painters get when painting an entire army - if you get bored of painting red, paint a few Tzeentch daemons or Nurgle daemons to have a break.
Dark Angels: Commonly known as Space Marines: Alpha Release, Dark Angels have always played second fiddle to Space Marines. Nominally a bikes-n-Terminators army, they have basically strictly inferior options for both to their cousins in Codex: Space Marines or Codex: Grey Knights. They have some unique gear, for sure, and they can pull some interesting tricks (all revolving around one piece of wargear, the Standard of Devastation, which turns your Boltguns into weapons of mass destruction) but are generally quite gimmicky and fall through if used against the same opponent a lot. They have a very grim, gothic feel - even for Space Marines! They get the whole Space Marines range plus some very cool extra kits for their Bikers, Terminators and some other specialist units, although they inexplicably lack access to some of the Space Marine gear. Apparently they have a new Codex on the way, which could do a lot to help them out. They're also in the starter set, and it's a pretty good deal; all of the units in it bar the Company Master are fairly good, and you can pick them up uber-cheap if you don't mind having a lot of the same model. They also have a focus on Plasma weapons and anti-Chaos rules, making them a pretty good bet against other 'traditional' Marine or Marine derivative forces (i.e. a Chaos, Space Wolf, Blood Angel or Space Marine army built around a core of flexible superhumans in transports or on foot, with some support elements).
Dark Eldar-- Dark Eldar are a very, very shooty army. They can absolutely devastate all manner of targets under a deluge of Poisoned shots and Lance fire. Rare is the enemy that can stand 18” from a Dark Eldar army and live to tell the tale. The trick is reaching the enemy to fire those horrible guns; while Dark Eldar are very fast, they’re also extraordinarily fragile per-point. Their vehicles are all Skimmers, and they can save a lot of shots through Jink, but if anyone shows up to the party with a Heavy Flamer or a Smart Missile System, you can be in big trouble. They dominate the movement and shooting phases; while they have melee units, they’re very glass cannon in nature (moreso than the rest of the army!) and are ill-suited to fights that they can’t win in the first round. A total lack of Psykers can also leave you at the mercy of a strong psychic presence from your opponent, which while unlikely to lose you the game, can make things very inconvenient as you watch powerful buffs and debuffs get slung around the board with no real way to stop them. Their models are widely regarded as exquisite, although you will tend to need a large number of vehicles to help you move around the field and protect your fragile infantry.
Eldar-- Fast, devastating shooting, and fragile infantry inside very tough (but hardly numerous) transport vehicles. A lot of Eldar armies are based entirely around the Wave Serpent transport which is infamous for it's extremely capable shooting, but it’s very possible to bring an interesting and diverse army for Eldar. Each unit is very, very good at one specific task, and while it can be a challenge to get your units working in synergy (and their fragility and cost will punish you if you get it wrong), if you pull it off they can supply a hard counter to almost any threat. A painter's army; Each squad type has its own distinctive costume, and you can really go to town on Harlequins and some of the grav vehicles. A lot of their Elites units are finecast, so they're pricey if you want to bring a lot of Aspect Warriors, but they’re far from required and you can often make very convincing conversions from the Eldar and Dark Eldar plastic ranges.
Grey Knights: Paladins in space! A very elite, very low model count army, generally relying on their very much superior wargear to win the day (they tend to start expensive, but with very cheap and very powerful options which must be bought with care lest your ultra-elite strike force gets overwhelmed 15:1). Nominally a Space Marine army, but very much less forgiving; the standard Grey Knight costs around half as much again as a regular Space Marine, but shares the same defensive stats. They are quite challenging to master, needing a deal of good judgement in the distribution of Warp Charge in the Psychic Phase and a careful eye during list-building (while they get incredibly good deals on their wargear, good deals on things you don’t absolutely need aren’t good deals at all for very expensive models). In the new book, they usually end up being Terminator-based, and I can personally attest that they are a very cheap army to build simply through their elite nature (Paladins can reach upwards of 400pts for 5 models!). A lot of veteran players regard them as a poor army on the table due to their fall from ‘very, very powerful’ in the previous book; I disagree, and simply think they are very different now and perhaps more balanced than in their previous incarnation. Their models have a lot of details, and are supposed to have individual heraldry which offers a lot of scope and a very striking bright silver, red and white palette when painted in the traditional scheme; however, painting Force Weapons can be a challenge, and as the vast majority of their is either a Power-Armoured Grey Knight with a different gun or backpack, or a Terminator with a different head and icon, they can get repetitive. Easier for beginners than something like Daemons or Tyranids, but not an army I’d immediately suggest for a new player.
Imperial Knights: A very strange army indeed. Without a doubt, the lowest model count army, consisting of generally fewer than five towering Imperial Knights, huge mechanical walkers controlled by a nobleman pilot. A recent addition to 40k, they’re generally used as a ‘plug-in’ to a ‘normal’ army; whole armies of Knights are comparatively rare. They don’t follow the rules for vehicles as laid out in the rulebook at all, instead using the Super-Heavy vehicle rules, and have all manner of exceptions and new mechanics. They’re not awfully complicated, being big stompy robots with giant chainsaws, but they take some considerable co-ordination to avoid having them out-manoeuvred and ground down by anti-tank fire. They’re at least quite cheap (while Knights are expensive individually, you won’t see more than six on the table even in big games), but more of a tool to add to the more advanced player’s toolbox.
Necrons— Arguably the easiest army to paint. A basecoat of silver, a black wash and five minutes picking out details will look effective on a lot of your units, infantry and vehicle. That’s not to say that they have no potential; the fine and unique detail on a lot of the characters and elite units can be made truly spectacular by a willing painter. On the table, Necrons are a very forgiving army simply through their resilience and army-building flexibility; while lacking in extreme long range shooting, Necrons can make very convincing hordes, air forces, armoured spearheads, mechanised infantry forces, fast-moving melee forces or close combat death stars. They do have some oddball unique rules that, while simplified in their new Codex, can still be tricky for a new player to grasp (their vehicles in particular don’t like playing by the rules). Despite this, their resilience, large range of all-plastic kits and fairly basic core tactics make them a strong choice for a beginner, with scope to expand outwards into their fancier gimmicks once you have a stronger grasp of the game.
Orks-- Orks can get expensive financially as their infantry are so darn cheap – even a relatively low model count army is looking at perhaps 80 Boyz, and it’s not uncommon to see 120 or more belligerent greenskins on the table. Many players prefer to run a vehicle-based army, which Orks can do very well - and with the Ork vehicle kits being as brilliant as they are, with an easy-to-build basic chassis with sprue upon sprue of customisation options, it’s not hard to see why. Orks are quite flexible, if a little simple; they don’t have an awful lot of fancy things, but they can put out a fairly terrifying (albeit wildly inaccurate) amount of firepower backed up by strong close combat; every Ork, even one with the biggest gun he can lay his grubby hands on, would prefer to get stuck in if he can. They’re regarded as a very comic race, with a lot of gear that blows up or has random effects (from relatively safe items such as the Kustom Blasta weapons, to the epitome of wildcard; the Shokk Attack Gun, firing terrified goblins through wormholes!). Painting them can get boring through the sheer number of them, but you can get through a surprising number of Boyz quickly by ‘batch painting’ (painting a large number of models in stages as if they were on model; doing all the basecoats, then all the layering etc. on the whole group at the same time), and the Orky patterns of checks, dags and glyphs can break up the sea of green, brown and rusty metal.
Space Marines— Regarded by many as ‘boring’, Space Marines are the poster boys of 40k and are widely seen as the army for beginners. They’re forgiving on the field, very flexible regardless of army list (unlike most forces, where you choose to be a shooting or a combat army when you make your army list, most Space Marine units can pull double duties, holding back against an Ork or Daemon army but charging into a Tau or Eldar army), and have a huge range of plastic kits. They’re almost infinitely customisable in terms of fluff and painting, with 1000 Chapters of which only a fairly small percentage have been formally fleshed out as canon. Most Chapters tend to have a ‘theme’, whether the Greco-Roman Ultramarines, the Spartan themed Minotaurs, or the Mongol White Scars, which allows you to combine your army with other areas of interest if you so wish. Space Marines are the most flexible in terms of army-building, too; while rather too elite to be a horde, they can be mobile or static, melee focussed or ranged, mechanized, foot or hybrid, and their Chapter Tactics special rules allow you to tailor your army into something very personal.
Space Wolves -- Viking Space Marines. Another melee-oriented force, but concentrated more on brute strength than the mobility and skill of the Blood Angels. They generally operate as a close-range version of Space Marines, with a lot of little bonuses to close-range fighting and melee combat but somewhat lacking in the heavier weapons or the more diverse tools that Space Marines can bring such as Chapter Tactics or 'swiss army units' like Sternguard Veterans. Their aesthetic is a source of some controversy; they're very heavily norse-themed, but with an awful lot of wolf pelts and tails everywhere and a unit of Space Marines riding giant wolves (which is ridiculous and utterly metal in equal measure). They are basically the same price as Space Marines, being basically the same army but with units doing different things and the option to bring more models over transports (which, conveniently, price comparably with the extra 10 guys).
Tau Empire—If you like gundam, or indeed any form of mecha, then the Tau might well be for you. An incredibly versatile shooting army, the Tau Empire can bring a gun for every situation and then some. Where Eldar have a lot of very specialised units that are excellent at one role, Tau tend to have a few fairly generic units with a tonne of options to make them into specialists. They excel at long-range firepower against units of all types (although much of their most potent anti-tank fire comes on short-range Melta-class weapons; albeit still double the range of anybody else’s), but have absolutely abysmal combat stats and can suffer from morale and leadership issues. They’re also home to some of the coolest sci-fi names in the game, boasting such gadgets as the Multi-Spectral Sensor Suite, the Puretide Engram Neurochip, Impact Repulsor Fields and Cyclic Ion Cannons. Widely regarded as one of the most powerful races in the game as their forte, high strength high volume firepower, is rewarded by the rules framework and their weakness, close combat, tends not to be as powerful an option anyway. They can be tricky for a new player to master as they have a fairly central mechanic of ‘Markerlights’ to mitigate their somewhat low accuracy and to crack enemies hiding in cover as well as their almost-unique Jetpack Infantry unit type, but they still make an excellent force for beginners due to the sheer versatility of the various Battlesuits and the strength of their shooting. They’re reasonably cheap to build as an army to boot.
Tyranids-- Tyranids are possibly the most expensive 40k army simply due to the number of models you’ll need. But oh, how many models! Tyranids are a truly terrifying horde army, easily able to outnumber even Orks or Astra Militarum with waves of ravenous sickle-armed aliens intent on eating everything in their path! An interesting army to paint as they are entirely biological; there are some very impressive Tyranid models out there using hot glue guns, varnishes and glazes to recreate drool, digestive fluids and all manner of fairly nasty glistening alien-ness (really, there’s no other word for it!). That’s not to say you have to be an expert modeller and painter though; a simple basecoat and wash for the flesh with a layered carapace will be absolutely fine in most cases, although a lot of Tyranid players never fully paint their collections through sheer exhaustion. On the tabletop, they are a very versatile army that have been given new life and a lot of flexibility by a spree of additional releases, comparable to DLCs, from Games Workshop and Black Library. They tend to go for quality over quantity, especially in their shooting, but it’s not uncommon to see armies of huge hulking monsters (so-called Nidzilla builds), and they have all manner of ways to get within arm’s reach; burrowing serpine or worm-like Raveners and their gigantic cousins, Mawlocs; swarms of insectoid or chiropteran Gargoyles and Harpies; or plain old carpets of scuttling horrors. I wouldn’t immediately recommend them to a beginner; they require a fair amount of skill to synergise effectively, and have a completely alien morale system (they are totally fearless as long as they stay within proximity of the larger ‘synapse’ creatures, but are prone to reverting to their bestial instincts and going out of the player’s control should the central synapse links be too far away or killed).