1- Rastakhan, Lord of the Zandalar Trolls
Not so much the character as the culture he represents. I'm not crazy about ZG as an instance, but I thoroughly enjoyed the lore on the Zandalar tribe that came along with it. From what Blizzard has fleshed out, they sound pretty badass. Maybe its just that they refer to paladins as heathens, but meh.
2- Thrall
My faction leader, right or wrong. It will be sad indeed to see him play a less active role in leading the Horde come cataclysm.
3- Jaina
Easily my favorite Alliance character. More than any human in game she is responsible for the victory at Hyjal. Shame she plays second fiddle to a jackass like Wrynn.