2200+ arena rating representation. Keep in mind, that Druid have more % then DKs, but Druids also had 3 viable specs to play in high rated arenas, DKs only had one, so if we would even those % between all of the Druids specs, that would make it more like DKs %, same goes for Paladin and Rogue, Paladins had 2 viable specs while Rogue really only had 1.
Druid 15.2% (152)
Paladin 13.2% (132)
Priest 11.2% (112)
Hunter 9.7% (97)
Shaman 8.8% (88)
Warlock 8.6% (86)
Warrior 8.4% (84)
Rogue 7.6% (76)
Death Knight 7.4% (74)
Mage 5.3% (53)
Monk 4.4% (44)
(Credit for "Arena Representation" statics goes to Dolci, Kel'Thuzad - US)
Sorry for long post on just 1 comment but i had alot to say for those who think that WoW is/isn't balanced.