Basically, Superman's power level jumps around a lot. So does Goku's. Supes vs. Goku boils down to "at what point in each's career of ridiculousness are we talking?"
The entire premise is pointless, but it doesn't stop people from trying.
See also: "it was done in a crossover once, and this settles the argument completely."
And: "not reading the thread (or apparently the title) and assuming it to be an actual vs. thread."