General guidelines: Chaos's strength is in its Troops and Heavy Support, while most of the HQ, Elite, and Fast Attack options are kind of meh.
All five of the Troops Choices are good, but Noise Marines tend to get a bit expensive, and Thousand Sons are prone to being Outmaneuvered and Assaulted, so the other three come out a bit better. Spamming Troops Choices, with a couple on Foot to form a Firebase and hold Objectives on your half of the Board, and a few in Rhinos, to go on the offense, is pretty hard to go wrong with.
The Defiler is Soooo Close to being good, but as it stands, is not so great.
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HQ: The Chaos Lord is the weakest of the three basic HQ Choices. He's not particularly bad, he's just not particularly good, either. Most Players go with a Sorcerer or Daemon Prince instead. Everyone talks about Lash of Submission, but once your Opponents figure out how to cope with it, it's really not that big of a deal. Warptime and Wind of Chaos are the Powers I see used most often. Note that the Chaos Lord kit can also be used to build a Sorcerer.
Elites: Terminators can do alright if you've got a Land Raider for them, or as a 3 man "Suicide Squad" to Deepstrike in, hit something with Combi-Meltas, and then soak some Firepower.
- Chosen are probably the best Elites Choice, but again, can get ridiculously expensive very fast.
- Dreads are mediocre. Expensive, unreliable, and not as durable as you might think. They are pretty cool, though.
- Possessed just suck. No two ways about it. If they got to roll for their ability before Deployment, they'd be OK, but as is, they suck. I use them anyhow, because the Models are awesome, but I must recommend that you simply mix those bits in to your regular CSM Squads or something. This was actually one of the points that most angered established Chaos Players when this Dex came out: Possessed got their best Models ever at exactly the same time as they got their worst Rules ever
Troops: CSMs are your basic option, one of the best Troops Choices in the game. I recommend at least one Squad of 10 in a Rhino, with two Meltaguns and a PowerFist/Combi-Melta Champion. I usually stick to the Icon of Chaos Glory, but the others have their uses.
- Berzerkers: Forget any of the Ranged options, here's all the Anti-Horde you need. Possibly the only Troops Unit in the game that can take on an equal Points Unit of Ork Slugga Boyz in Combat and come out on top. Don't bother with Plasma Pistols, just take a Champ.
- Plague Marines: Possibly the best Objective Holders in the Game, especially if they're in cover. I like two Plasmaguns and a PowerFist/Combi-Plasma Champ, myself.
- Noise Marines: Cool, but they get expensive really fast. Much more worthwhile if you tend to play against Armies without Power Armour, though.
- 1000 Sons. Powerful when shooting, especially against Power Armoured foes, so they complement Noise Marines nicely. Prone to getting swamped in CC, though
Fast Attack: Both choices are overpriced and underpowered. Just don't bother.
Heavy Support:
- Havocs: Meh. Expensive, and they can get shot up or tied up in Assault pretty easily. I've made them work, but the other Choices are so much better that they're hard to justify.
- Obliterators: Probably the most common choice. Resilient and flexible, these guys have an answer for anything.
- Predator: The Anti-Infantry version is great, the Anti-Tank builds get too expensive. Don't Possess it, the reduction in BS hurts.
- Vindicator: I may have mis-spoken about the Oblits, Vindicators are probably just as common. Basically a slightly less tough and flexible version of the Leman Russ Demolisher.
- Defiler: Really hampered by being BS and WS3. They tend to get Assaulted and ripped apart very quickly, and they pay Points for a lot of different things that can't really be used together. Very cool Model, though.
- Land Raider: Pretty much only to haul Terminators or Berzerkers in. Too expensive to justify as a Combat Tank or a Transport for anything less Devastating in Assault.
