Thassarian.
Wrynn is boring and is just a rehash of Anakin Skywalker. Bolvar was the only cool human until they killed him. Janna is cool, but too much of an orc-lover to really lead the alliance.
Thassarian is the only human with any depth of character left. Therefore, he is literally the only hope humanity has.
Come on blizz, its not all set in stone... lets see this happen.