super vegito
Depends on the version of superman you are using.
vegito
If the circumstances for both of them are optimum (Vegito at SSJ2, at full health and with a tail and Superman prime fully charged with solar energy, wearing his solar energy collecting suit) Vegito would probably win from Superman prime.
super vegito
Super Vegito
If Vegito became a Super Saiyan 4 he would be far stronger than Gogeta.
superman
Super Saiyan
Superman. Unless super woman pulls out kriptonite. (She isn't effected by it) Superman. Unless super woman pulls out kriptonite. (She isn't effected by it)
Logically, Gogeta would win. Vegito and Gogeta are both fusions of the same two people, but in Dragon Ball GT, Gogeta became a Super Saiyan Four. Vegito has never reached this level of Super Saiyan, and should therefore have a lower power level and be at a disadvantage in a fight between the two.
Vegito. He could just blow up the universe by snapping his fingers(tht includes supermans source of power the yellow suns) and then teleport to heaven(thts assuming the explosion would even hurt him) with instant transmission and be done with it.
Gogeta and Vegito because all they would have to do is spirit sword his tail off . Both fusions are faster than him any way