Round One:
Now knowing these two they'd never fight as they both defend the Earth from all sorts of extradimensional and outter/inner worldly threats, but for the sake of argument for the fight we'll say that both Goku and Superman were found to illegal immigrants by the UN and since the world is overpopulated enough, the UN forces them into a battle to determine who is the better hero. The winner stays and is known throughout the universe as the powerhouse of the planet Earth and a god amongst men...the loser...deported into outer space.

Goku, being obviously upset at the U.N.'s actions in a moment of mental weakness sees Superman as not a person in the same situation but as the enemy in which he must destroy for his very survival. Skewed logic I admit but hey, not even Goku is perfect. Goku powers up his ki, the bright red aura of it appearing as flames around his body, the very power of it lifting up rocks and trees around him in a fantastic display of raw unbridled power. Supers steps back in a brief moment of shock but quickly regains his composure and leaps to the attack, busting a hit that could shatter Mars across Goku's jaw, knocking him forceably back into the nearest building, totaly demolishing it. Superman, not knowing the sayajin toughness turns his back on the ruins of the building, speaking to himself of how it is a shame that such a noble warrior had to die in such a futile fight. Superman also fails to notice that the rubble is moving and Goku is standing and is looking EXTREMELY pissed off. Round One goes to Superman.

Round Two:
Goku finishes powering up his ki, and ends up turning into a super sayajin again with the sheer amount of pisstivity he's feeling at these people right now. Superman, hearing the rubble shift, turns around only to see Goku with long blonde hair and a look of "you're about to die mofo" written all across his face. Before Superman knows what hit him (it was Goku by the way) he finds himself looking at the other side of the building three blocks down and his chest very bloody and bruised up. The only sound he hears is the almost indistinct "kamehameha...." Round Two goes to Goku