Superman is stronger than Goku.

Due to the slight ambiguity of the question, I am going to argue as 'who would win in a fight' and I'm going to base my argument on Goku and Superman only and not their friend's, allies, objects or motives. In the early days of Superman a lot of his powers weren't there, they were later invented to make him seem more impressive as well as fitting as a quick way of getting out of a situation (flight for example). In the Dragonball Series if it is not clear on the rules and limitations of powers it is hinted or alluded to. After post-crises Superman, writers re-evaluated his power and powers and stuck to them. They have been like that ever since. My point here is that Superman, in his current state, is known as the 'strongest being in the universe'. This is a fair statement but he can never improve himself now, in a legitimately believable way. Meanwhile Goku through intense and dedicated training is already the universes greatest defender. Whole races attempt to damage the Earth and/or those he cares about and fail. This is down to Goku already being the world"s single mightiest warrior through training and experience. On top of this through sheer concentration and willpower Goku is constantly breaking through boundaries and bettering himself. A regular move for Goku is the spirit bomb; he gathers energy from the world and uses it as an immense force to destroy his foe. Very few have survived this attack from him. He has not only become a Super Saiyen when so very few achieved this he has reached Super Saiyen levels 2, 3 and 4. If this is not enough he can use the fusion technique. He can combine himself with another powerful warrior to (for a short time) become a single overpowering being. Superman possesses incredible speed that could outrun pretty much anyone. On the other hand if Goku's speed is said to surpass millionths of a second. Not only this but if he is in a hurry he uses instant transmition (which is basically teleportation). He can occupy any space in the universe, use instant transmition, and literally occupy another space of his choice in no time at all. Superman obtains his powers from the sun, without this he would simply be just like any other human. As it is, if he is anywhere near green kryptonite it renders him immediately and completely incapacited. Superman not only has to worry about green kryptonite but also has to be concerned about other forms that have negative effects on him. Depending on the colour of the kryptonite (which I may add is broken parts of his OWN planet) Superman can lose his inhibitions and become violently bipolar or lose his powers permanently. Goku's powers are his own, he doesn't need anything to have or keep them and so has no such limitations. Granted at the beginning Goku was born with a tail that caused him extreme pain if pulled however, he had his tail removed that weakness is obviously eliminated. It's common knowledge that Goku learns from experience, meaning if Superman does happen to have the upper hand, Goku's tactically superior mind and higher level of combat experience would soon give him the upper hand. So, I think it's clear that Goku would win in any competion between these (or any) pair.