I like the Alpha Legion, at least when they're being handled by competent writers. I'm especially fond of the implication that they're all just doing their own thing and have long since lost sight of whatever overly complicated bullshit plan Alpharius and Omegon were trying to pull during the Heresy. It gives a lot of space for Your Dudes, so you can do an army of closet loyalists, renegades, all-in Chaos worshippers, or space pirates and it makes total sense.
I also like the Emperor's Children because the idea of Noise Marines high off their gourds on warp dust and killing their foes with weaponized dubstep amuses me and I like the Hellraiser vibes they give off in the older art. I'm hoping the range refresh that we're probably getting come 11th leans into that body horror aspect a little more, like the HH Kakophoni models do.
As for minor warbands, the Purge, solely because they're what would happen if you gave Judge Death a pack of Chaos Marines and told him to go nuts.
CSM have always lent themselves well to /YourDudes/
Black Legion for all their faults are great for this, as they’re just warbands sworn to Abaddon, not a marching army. They literally take anyone, unfortunately the Red Corsairs do the same while also retaining soul, character and not being mutts. Bonus points if you just make True Sons who stayed in the SoH colours and told Abaddon to pound sand.
World Eaters shattered, go wild, HH colours are better though (this is true for all of them)
Emperor’s Children shattered, go wild, they have a hundred colour schemes as is, yours will be the best though.
Word Bearers, Hosts fight each other all the time, some Hosts haven’t even been to Sicarus. Unlike what some (retards) say these guys also use the cult units, they just single out squads who veer too closely to one god and make it so they don’t get promoted.
Iron Warriors, every Warsmith thinks he’s an evil genius who will build the strongest micro-empire. Lots of potential.
Death Guard, their 8th codex really went the extra mile in showing that the company system from the Great Crusade is still alive in this legion. So they’re more ordered but each Vectorum is its own can of worms.
Thousand Sons, same with the DG that 8th ed codex really fleshed out the Thrallbands. The Ahriman book off-handily mentioned getting regular warbands as allies/indentured servants/slaves/ manipulation victims and I think that could be a great idea for an Apocalypse game.
Alpha Legion, you are being deceived and every warband thinks they’ve got the true orders.
Night Lords shattered, go wild, in midnight clad of course.