The class, which is considered most unbalanced would be warrior. I didn't believe warrior was so strong, up until the point when I started playing one...ownage. And imho due only to one thing: speed. I have absolutely no prob with a warrior slashing through me like a hot knife in butter, if he gets up close. The problem is, they get up close too damn fast.
Movement speed should be nerfed, so that they can't catch up with assasins and archers.