I'll awnser for my part in the PvP since i don't PVE much. From experience in PvP, the hardest i have played and the one it took the longest to learn was the feral drood. I am NOT saying it is unplayable, it IS playable, but even when you learned it well, timing your abilities and cooldowns for the max DPS on people is still hard. Managing your instant heals so you don't waste them, using deff cooldowns to stay alive and survive bursts, that is that i think is hard, you can do it, but it takes a lot of time to master it well, and when you do you can 1v1 any class, simply because the feral has one of the biggest survability. I did carry A LOT of people in Pandaria, in 2's and 3's, and i don't think i could have went that far without a Feral druid

ALSO, i think mastering Shadow Priest in PvP is also * Hard * Because it has a lack of survivability. Yes it is good and has a decent damage, but mastering how to stay alive, kite well and use your dps in an efficient way is hard IMO
