Tbh, its not about the class. You can play a good class/spec, but play a shitty comp. You can play a decent class/spec and do much better.
Best example is RMD (my fav comp). Its not op cause of the rogue, its the synergy between all the classes together that makes it a tier #1 comp.
Mage druid x is just so powerful. So much cc already, now combine a rogue. Cyclone/blind/poly/deep/cs/garrote/Cheap shot/kidney/roar
You have so much control. You have so much stability and mobility. So many defensives, all your offensive cds has the same cd (1min).
But if you put 3 retarded pwow classes into the same team, you're unkillble almost. *Cough wls cough*
But to answer your question, id say arms warrior and aff lock.
Pwow, not retail.