Pre Crisis Superman is the strongest force in the galaxy. He would win. He routinely wrecked gods. Post-Crisis (nerfed) Superman would be beaten by Goku. However, it would be a good fight until goku hits super sayian. Post crisis superman could BARELY destroy a planet. It's all about what incarnation of superman you are talking about. If the person writing the "script" remembers that superman is one of the smartest beings in the universe then it would be a better fight...because goku is dumber than a box of rocks.
However Superman and goku would never fight because Goku would just sense the good in superman and Superman never would punch first. They would just join up and beat some greater evil. The better question is Superman vs Vegeta