I've been cranking out lists for a while now and I think whichever list I take will have 2x Keepers. They're IMO the best choice when it comes to staying around combined with killing power, plus their array of spells and command abilities are great. While I think some people have put forth good explanations why they would like 3, I'm not so sure because then the lists get skinny.
For Battleline, I'm really leaning towards 30x Daemonettes and 2x5 Hellstriders as a solid all-around, but I can definitely see 2x30 and 5x Hellstriders if you're running Epicurean Revellers.
I see that some people say that Fiends are bad. I'm not so sure on that statement mainly because 420 for 6 gives you a very solid unit that poses a threat to everything in the game, especially multi-wound units. With double-strike and ASF from a Keeper nearby, that pretty much spells instant death for any monster in the game. Not that the Keeper needs that much help doing it itself.