Well from the HH FW books, we have MkII Cited as the most efficient armour at the time. We know the MkIII Was an over-taxed, high maintenance type due to it's up-armouring.
The MkIV is clearly cited in many sources as the most advanced type in general distribution at the time.
Likewise we know the MkV was a patchwork design; the hows whys and exact current chronology, we do not know, but basically, it's the on-hand or easy to make parts from Mk II, III and IV, with a head from the Termie project (split thread anyone?).
Calling Beakie armour MkVI should tell us it follows MkV in development, if not production, but this is not exact and it could easily be that the VI was developed before the MkV and the naming conventioned sorted out later. Likewise the MkV could well have been a contingency protocol which had been on hand since before the MkIV for all we know. We do not see very much of Heresy Armour in print, but likely they're overall of poor fit and finish, with some lucky Astartes finding some MkIII or MkIV Surprises in their rush-job replacement suit.
MkVI, is either a dog-standard suit, or an advancement or at least refinement of the technology of the MkIV.
Personally, I always got the sense that the standard-40K MkVII was a stopgap, de-enriched, moneky-model type intended for easy production in place of more advanced MkIV and VI types. The MkVIII seemed more like an improved MkVII, maybe even a direct, possibly modular upgrade. it seems to offer better protection to the Progenoids in apocryphal sources and it *looks* better protected, but it's really hard to say. My feeling is that it's better than a VII, but not so good as a IV.
So what about the odd marks? If we rule out consideration of Thunder armour, as we should because it is obviously less capable in all references I know of, then we only have some odd modifications and inferred transitionary and hybrid types left to consider.
Aegis and Artifacer armour are clearly modifications of other known patterns, though the Grey Knights seem to have their own kit all the way around and we can assume they get the best gear there is. I'd peg them in as wearing a suit as advanced as a IV, with VIIII refinements, but shy of MkIII Armoured protection overall, but that's just my theory.
We see some clearly transitory and hybrid IV-VI and VI-VIII models, but I haven't heard of any in the fluff. People sure build them though. By 40K, I'd expect the legions favouring the VI suits to be either making basically a MkVII suit with a Beakie head and a few odd refinements or maybe having access to advanced technology. In practice, I'd actually consider hybrid suits as MkVs in spirit, if not practice, but likely with better fit, finish and wear over time.
I think longevity of different types would play a role as well. I Look at the MkII, III and V as certainly mass-produced, short life-cycle (in 40K terms) items. Build as many as we can to support needs NOW! and replace them as we go with the tech we have in abundance. Any left in 40K are true relics, or essentially modded VIIs or earlier marks which have been essentially gutted and rebuilt as VIIs internally.
The IV, VI and possibly the VIII if you're an optimist (why are you playing 40K?) look from the fluff a lot more like long-haul legacy equipment built for the duration. Stuff that is meant to last a long time, with a high quality of fit and finish, which is not to say that other marks are ersatz works by a long shot, but that these are higher-quality suits. You're not going to just scrap a MkIV when it get's banged up; whereas if a Marine's MkII or III takes a pounding, you may as well scrap it for parts and give him a new one because it isn't built to be fixed like that and/or economic repairability is low. But by the time you're in the Heresy and much beyond, any suit is precious and you keep your patchwork MkV running as long as possible.
Post Heresy, i see production along two lines; the Holy crap we're drowning lines turn out MkVIIs like sausages and the Gucci line (Quality is remembered, long after price is forgotten) trickles out MkVIs to the best-connected legions, so long as it makes economic sense for them in the post-technological reality of 35-40K, until the VII is the standard suit because the mechanicus lost the data in their last HDD crash.
As things recover, the tech of the IV and VI may as well be lost, but you can start with the VII and improve it and get the MkVIII Errant armour, again more or less for the best set-up and connected legions, but a limited issue item. Demand will be lower, because by now, every issue item is a cultural relic of personal significance, even your comparitively primitive VII, which in balance, I take as inferior in terms of efficiency to a MkII. But again that's me trying to make everything in a chaotic canon all fit in a way that makes sense to me. Also by now, most MkIII suits have been cannibalized to keep MkII relic suits running, or have worn out themselves. Short of Someone like the Iron Hands or Imperial Fists making them, I'd peg MkIIIs as the rarest type in service in 40K, while new "effective MkVs" and hybrid suits should keep showing up out of necessity and as a result of bespoke modifications, mostly with MkIV, VI and VIII parts.
So what's left? Well the odd stuff.
We have the Space Wolves' "Wolf Helm" which you can look at as either proof that the real deal MkVI is something of a lost art and they want to recreate it, or a further improvement. Personally, I look at it as support for my theory of Sub-Stanard MkVI hybrids which are just VIIs under the skin.
We have the Chaos suits which are by now either warp-twisted relics (1000 Sons, Plauge Marines, ect), Hybrids (many, but especially Night Lords, so it seems from some novels), possibly a few instances of an exclusive pattern (which would seem to fit the HH take on the Alpha Legion's MO and makes sense of the Iron Warriors too) and I think a great deal of mass production from daemonic/eye of terror forge worlds (Which is where I peg in stuff that gets issued to folks like those 30,000 Khorne Berserkers (low-maintaince, replace when broken items).
It follows that the Iron Warriors make their own Armour, likely a hybrid/stabilized take on the MkIII, which deals with wear and tear better.
How good is any of it? The Warp does what it wants, so forget trying to rate the corrupted suits. The Night Lord and similar hybrids are going to vary individually based on what's been captured. There is some visual evidence of Emperor's children going for looks over substance (Shocker), so I'd rate their protection at least as inferior to even a MkVII or II, possibly in line with Thunder Armour, but efficiency as probably quite high, but again; it's going to be corrupted in many cases: so whatever.
The Alpha Legion's suits will likely be built as top-rate, probably the equal or superior to HH MkVI suits in stealth, sensors and efficiency and maintained in the field on a catch-as-catch can basis for those who are spread out in cells, sot hey come to rely on skill over steel as time goes on. The Iron Warriors will be building for mass numbers, but tempered by maximum protection; I'd expect their suits to sacrifice efficiency and perhaps longevity due to their normal MO keeping them close to base areas and massive stores ships. But I think that in The Long War, they'd come to value longevity over time and might produce suits of varying quality for troops esteemed differently; the crap for the new guys and the better quality, longer-lasting stuff for the guys *NOT* in the front rank of the forlorn hope.
Berserker-type mass produced suits? Cheap mass-produced junk. if it breaks, they make a slave fix it, they MAKE IT WORK, or their RAGE makes it work, at least long enough for them to contribute in some way to the blood whose origin Khorne cares for, not very much.
Anywho, just my opinions from a long time of reading fluff and trying to make it all make sense. Combined with a fair hunk of back ground in military equipment history.