Id say priest and warlock.

A shadowpriest + warlock is the most insane + shadow damage for the lock, and you will nuke anything. And if you go UA then you have dot protection for 2 sets of dots.

Holypriest + warlock is a very high survivability rate and the ability to just dot up 10 mobs and heal through it.
Plus soulstone + rez is a lifesaver.