The big comic book question always seems to be 'who would win in a fight between Superman and Batman', but I think that's a silly question. Superman is too powerful. This is a better question: who wins between Goku and Superman?
Their sheer power is more equal.
So here's the situation. Goku is eating at McDonalds, scoffing down a Brazil burger or something. Superman is in the queue to get a Crunchie McFlurry. On his way to put his rubbish into the bin, Goku bumps into Superman and shit gets real.
Point being -- there's no preparation. This is just an on the fly fisticuffs affair. Who wins?