Monk. That's not because the concept is bad, because it does fit a lot of settings. But, the Monk is invariably an afterthought in the game, neglected in terms of mechanical support once it's basic iteration comes out in favour of other classes. And with unarmed combat that isn't functionally identical to armed combat having always been done in a complicated manner, that means it's a rules-intensive class in a way I don't like. Further, once you've decided you have to have a "fighting-without-weapons" class, then you end up making usre other classes that would have training fighting unarmed are really bad at it. Champion pankratiast who also fights in the front rank of the phalanx is right out.