I'd go daemon allies since they are still pretty strong these days. Or khorne daemonkin to take really powerful khorne hounds.
Its a pretty big subject and depends on playstyle a lot so I will point you towards some good posts going on these days about chaos marines/daemons/renegade tactics.
Here is a good writeup to get up to speed on renegade tactics (basically cultist army) from a recent battle report:
http://www.dakkadakka.com/dakkaforum/posts/list/676897.page
Here is a good chaos tactics thread going on right now:
http://www.dakkadakka.com/dakkaforum/posts/list/677691.page
and another smaller one worth reading:
http://www.dakkadakka.com/dakkaforum/posts/list/677809.page
And also this is a really great tactical breakdown of
CSM/daemons beating Eldar with the key takeaway being take a couple
lvl 3 sorcerers and roll on telepathy powers to get invisibility and shrouding:
https://www.youtube.com/watch?v=rhNKWAH9Sj0
Invisibility is your friend
Note - don't go with the bastion like he did just get normal void shields since apparently he played it wrong (admits it in comments but says void shield would have played out the same and probably would have been better)
If you don't have the void shield model don't worry it is out of production - just scrap build one.
He takes Belakor, and 2
lvl 3 no-mark sorcerers on bike that roll on telepathy so good chance of getting 3 psykers with invisibility.