Eh. What people don't get about the Dragonball Z Universe is that their physical stats greatly lag behind their Ki output stats.
Master Roshi can planet bust a moon... while his physical stats are WELL below your average character with super strength. Yet his punches deal about the same level damage to an opponent as his energy attacks.
Ki attacks either are largely ineffective on people, or martial artists in the dragon ball Z Universe develop some level of innate ki resistance from their training.
Physically Superman just outclasses him too much... and also, honestly probably outclasses him in energy projection. (though not by nearly as much.)
Superman has never destroyed a planet... but he's Superman. Why would he. (He has destroyed a moon through in a manner like friexa, but just through pure strength.
It's worth noting that his heat vision is hotter then the sun which has been shown as something that can kill DBZ characters with ease, and he's used this heat vision before to move planets.... while under a red sun (which HUGELY weakens his powers), he's covered an entire planet in heat vision and can burrow through earth far faster then Freeza's core detroying energy blasts can. (Who is well well below Vegito, but it's just pointing out how Frieza's planet busting feats aren't in the least impressive vs superman.) His heat vision is generally considered stronger then his fists. (It's also a burning/drilling type energy, not explosive like DBZ.)
I'm no great fan of superman, but he should take a battle vs any DBZ character pretty handily. The only chance Vegito would have is Superman's innate "carefulness/stupidity" in combat.
He tries to fight to his opponents level to avoid hurting them, so if he H2H's vs Vegito for a while and ends up unharmed and assusming Vegito is completely weak, he might be stupid enough to take a planet busting blast head on without dodging. Of course Vegito isn't known for his smart fighting either. Seemingly combining the worst aspects of both characters. The Arrogance of Vegeta with the Playfullness of Goku.
If we're talking each character wants to take the other down/kill each other/doesn't hold back.
Superman is just too fast, two strong and his heat vision is something Vegito just can't stand up against.
Or he could just fly goku into space if they fight in an uninhabited universe. Superman can hold his breath and there would be noone Vegito coud Instant Transmission to.
Of course a full powered superman would be a boring fight/character, since he'd just lobotomize all of his enemies from orbit. Like Justice Lords superman.
Dragonball Z Characters are a lot like Wolverine, in that their power is greatly overrated. It's just worse because unlike Wolverine, DBZ characters have high levels of power.
Just not Superman/Silver Surfer levels of power.
