In my opinion from what I've done.
Yor'sahj (easier on healers and dps)
Warlord Zon'ozz (You need good everything, the tank will be getting hit for 100k at CTC and in full H t12, healers have to push big numbers and tight enrage).
Hagara (people able to adjust on the fly, and very good burst healing, also good communication between tanks and healers).
Ultraxion (Baller dps, heals, tanks can be meh)
Warlord (haven't done it)
Spine (sounds like a bitch, I haven't done it))
Madness (I don't want to know)
((I don't raid 25's so this might be a bit off its what I heard.))
[Today 06:48 PM] Ion:swimming in a natural body of water ISN'T acceptable...it's momentarily tolerable