I personally think that superman would win, but not easily. In DBZ they just keep gettin stronger, but i remember one episode in which piccolo and goku were learning to drive and had trouble lifting a van. Anyone who knows Superman should know he ALWAYS holds back unless he gets super pissed. His heat vision can penetrate anything and he is so strong he moved the moon out of the way of an asteroid. All goku could do would to blast the earth's core which would cause it to self destruct. Superman can take the sun's heat and that's basically what the kamehameha wave is. Superman is indestructable, with the exception of kryptonite or magic. Goku can be pierced by needles, while superman's skin makes needles bend. Superman can go back in time with speed, goku is faster than the speed of light. Overall, I think that they are pretty much evenly matched in speed, but Superman has a more arsenal of weapons. Overall, I think it would be cool to watch, but superman all the way.