I have played shaman, lock, warrior, hunter, and rogue to 85.
I keyturned until I started playing my rogue. I HAD to keybind just to play one effectively. They have many situational abilites that have to be on immediate call when the event does arise.
Easiest is mage. Arcane is a joke in terms of play/ramp up (lulwut?). I hear about frost mages being suberbly difficult in pvp but my mage friends say thats just what mages do to keep from getting nerfed, its pretty damn easy (shield, root, stun, do damage<---priority)