Warlocks are obviously the most valuable as they can push both bosses of the map AND self revive, plus they have song of flame and othr helpful stuff. Then Titans as the bubble shield helps and they can also push bosses of with their grenades. Hunter's really have no special skill. I'd only pick a Hunter over another class if it was a 30 and the others were 29, apart from that, if I need 2 players, and I have one of each class all level 30, Hunter get's left out every time!