Some likable actors might consider this quality a liability, because it's hard to imagine them ever playing an unsympathetic role.
I think all of these guys are at least a little likable (even John Travolta, if you can ignore the Scientology). But I voted for Will Smith, Greg Kinnear, Shia LeBoeuf and Owen Wilson. Sadly, I'm not sure what will happen with Owen Wilson's likable image now, though ...
At one time I would have voted for Tom Hanks, but for some reason I feel less that way about him these days.