So I've been playing a number of different builds using Abaddon and all the cults recently, usually fully mechanized in Rhinos with some terminators, obliterators, and demons in the mix. After a couple tournaments and various friendly games, I'm still moving things around. These are some observations of the different units in the army, by themselves and in the context of the rest of the force:
Abaddon and Slaanesh Terminators - After two games in a tournament yesterday where Abby was barely able to kill half a squad before dying (even with a full bodyguard), I'm putting the brakes on how I use the big guy. Here's what typically happens when I deep strike him with my slaanesh terminators into battle: my opponent fires everything they have at his unit, using heavy weapons as well as disembarked special weapons (plas/melta), wipes out the terminators, wounds Abaddon once or twice, and charges in with assault troops or I charge him in the next turn. Abaddon kills maybe half a squad with Drachnyen, they break, he can't sweeping advance, and he's left out in the open all over again, squish. That's if he doesn't kill himself with his own demon weapon. And it hasn't happened yet, but it's quite possible that the terminators break from all the shooting wounds in some game and Abaddon has to go with them. I contemplated putting them all in a land raider, and I still might try that, but I'd be taking away points from somewhere else. Not being able to do a sweeping advance means a lot more these days, when the loser breaks so often due to the negative Ld modifiers. I think I'm going to ditch them for a while.
Thousand Sons - These guys seem to work just fine without their own rhino, and do best in the largest squad possible (9 + sorceror). I gave up on bolt of change and gave my sorceror doombolt to streamline their usage and add more dakka. Despite the sorceror's force weapon, they can't stand up to much assault and so I'm thinking of pairing them with Abaddon and using them to protect home objectives.
Berzerkers - As long as the enemy doesn't get too many shots into this squad, these guys can fuck shit up pretty bad. I decided against giving them plasma pistols, since furious charge and the champion's power fist is usually good enough anti-tank for them, and I don't want any more pointless wounds on the unit than is absolutely necessary. These guys would also probably do better in a land raider than a rhino.
Noisemarines - I'm going to try dropping their rhino and using these guys as a solid anti-infantry firebase, just like I'm starting to do with the thousand sons. They're better in assault than the thousand sons, but could probably use an anchor like Abaddon or another character. So now I need like 7 or 8 sonic blasters. Haven't decided whether to give them a blastmaster or not or whether to keep the champion's doom siren.
Plaguemarines - If they can get on an objective in cover, they can usually hold out against a lot of shooting and assault. I want to try increasing their squad size from 8 to 10 just to make them that much more annoying. A rhino would still be useful for them to get their meltaguns into proper range of land raiders and such.
Obliterators - Having these guys in 3 separate units of 1, and therefore able to target 3 different units, is nice but a little bit of a liability in kill points missions (especially in custom missions when non-troop units are worth more KP). I'm still getting the hang of when I should deep strike them and when they should start on the board. They do well when they get to come in at close range and blast land raiders or other vehicles with melta.
Flying Lash Prince/Greater Demon - T5 and a 3+/5+ save means the demon prince never lasts very long. He's not so special in assault, either, compared to some other monsters out there. I'm starting to like the cheaper greater demon better with T6 and a 4+ invulnerable.
Lesser Demons - I think I'm over these dudes for a while. They are annoying for an enemy but always seem to lose combat and then suffer even more wounds from being fearless.
So here's a possible future list, with all these things in mind:
Sorceror - mark of slaanesh, lash of submission, bike
10 Berzerkers - champion with power weapon, rhino with extra armor
10 Plaguemarines - champion with power fist, rhino with extra armor
10 Thousand Sons - sorceror with doombolt
10 Noisemarines - champion with doom siren, power weapon, 8 sonic blasters, blastmaster
Alternatively I could swap out the sorceror for a defiler.