This is why I don't care for the new codex. Before you ask what Troop Choices you should take, you should ask to which Legion the army belongs. Despite what the Codex says (and anyone who knows and loves the Traitor Legions will attest), they don't fight in these mismatched warbands, letting their allegiance to their gods go unchecked-- Plague Marines will NOT march in stride with those devoted to Tzeentch, nor will Berserkers fight alongside those dedicated to Slaanesh. The rules may let you, but the fluff won't. Even the blurb in the current Codex regarding how in a Black Legion army, cults will fight alongside each other-- it's not entirely right. In the scheme of a Grand Company, it's possible-- a couple of cult squads out of a thousand Space Marines is plausible under a particularly brutal leader whose sheer intimidation rules out infighting-- but in the kind of warband that the new codex describes... the army would fight itself as much as (and as readily) as any enemy, and in some cases, probably before the enemy.
I so very strongly dislike the new Codex purely for that reason-- it not only encourages people to play armies against the long-standing background, but almost requires it since some of the Legions are no longer functional as independent armies. Thousand Sons come to mind-- you can't have a functional 2000 point army that has 48 wounds with 3+ saves. It doesn't work-- the mechanics of the game are such that even with superb tactics, the odds are overwhelmingly stacked against you. Iron Warriors and Alpha Legion armies too have lost their defining traits, and above all else, I think the World Eaters have lost what will make them unique. Expect to start seeing squads of Havocs with the Mark of Khorne and assault weapons to back up a Berserker charge.
To be blunt, here's how I look at it. Your options should be, depending on your Legion alignment (or renegade Space Marine Chapter, for that matter):
Alpha Legion
--Chaos Lord, Chaos Sorcerer, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Chaos Space Marines, Chaos Bikers, 0-1 Raptors, Chaos Spawn, Havocs, Predator, Defiler, Land Raider.
Black Legion/Sons of Horus:
--Abaddon, Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Greater Daemon, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Chaos Space Marines (Icon of Chaos Glory only), ONE type of the following unit, which must match the Chaos Lord or Daemon Prince's alignment: Khorne Berserkers, Plague Marines, Noise Marines, CSM with Icon of Tzeentch; Summoned Daemons, Chaos Bikers, Raptors, Chaos Spawn, Havocs, Obliterators, Predator, Defiler, Land Raider.
Death Guard:
EVERYONE must have the Mark of Nurgle or an Icon of Nurgle.
--Typhus, Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Greater Daemon, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Plague Marines, Summoned Daemons, Chaos Bikers, Chaos Spawn, Havocs (no heavy weapons), Predator, Defiler, Land Raider.
Emperor's Children:
EVERYONE must have the Mark of Slaanesh or an Icon of Slaanesh.
--Lucius the Eternal, Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Greater Daemon, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Noise Marines, Summoned Daemons, Chaos Bikers, Chaos Spawn, Havocs, Predator, Defiler, Land Raider
Iron Warriors:
--Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Chaos Space Marines, 0-1 Raptors, Chaos Bikers, Havocs, Obliterators Predator, Defiler, Vindicator, Land Raider
Night Lords:
--Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Chosen Chaos Space Marines, Chaos Terminators, Possessed Chaos Space Marines, Chaos Space Marines, 1+ Raptors, Chaos Bikers, Havocs, Predator, Land Raider
Thousand Sons:
EVERYONE must have the Mark of Tzeentch or an Icon of Tzeentch.
--Ahriman, Chaos Sorcerer, 0-1 Daemon Prince, Greater Daemon, Chaos Terminators, Dreadnought, Possessed Chaos Space Marines, Thousand Sons, Summoned Daemons, Predator, Land Raider
Word Bearers:
Everyone must have the Mark of Chaos Glory (what a dumb name... just call it Undivided like you have for the last what, 20 years?) or an icon of the same name.
--Chaos Lord, Chaos Sorcerer, 0-1 Daemon Prince, Greater Daemon, Chaos Terminators, Possessed Chaos Space Marines, Dreadnought, Chaos Space Marines, 1+ Summoned Daemons, 0-1 Raptors, Chaos Space Marine Bikers, Chaos Spawn, Havocs, Predator, Defiler, Land Raider
World Eaters:
EVERYONE must have the Mark of Khorne or the Icon of Khorne.
--Kharn, Chaos Lord, 0-1 Daemon Prince, Greater Daemon, Chaos Terminators, Dreadnought, Possessed Chaos Space Marines, Khorne Berserkers, Summoned Daemons, 0-1 Raptors (as, admittedly, they are rather choppy.), Chaos Space Marine Bikers, Predator, Defiler, Land Raider
Renegade Space Marines:
Honestly, as any of the above, but Red Corsairs/Astral Claws should follow the Black Legion rules, substituting Huron Blackheart for Abaddon in the list. Followers of Fabius Bile would probably be solely Undivided but follow the same general guidelines as a Black Legion army.
*sigh* I can't wait to gouge out my eyes when I start seeing army lists that have a Chaos Lord with the Mark of Khorne leading an army with maybe one squad of berserkers to back him up and otherwise be entirely devoted to Slaanesh for the sake of fire support. I HATE the new Codex... if you don't care about fluff, it's just bad... and if you do... it's merely passable as long as you resist the temptation to do dumb stuff with it. :evil: