Realistically speaking, Superman.
I'm agreeing with that more after watching what
>>5 posted.
While Goku is awesome and, to me, a better hero-thing in the first place, Superman's powers are and are meant to be limitless.
But then there is what
>>2 posted, which also makes sense. This argument is hard because there's no real numbers or way to prove who would win in a fight.
But unless Goku drove Superman away from the sun or something, I doubt he'd win :(