Most comic book creators thought Thor would win though, simply because he's got more battle experience, AND Mjolnir is a magical item...one of Superman's weaknesses. Oh, and Thor's a god while Superman's a man.
Here's Wizard's interpretation on how the battle would take place.
LAST MAN STANDING
|Superman vs. Thor||Art by Ed McGuinness|
|TALE OF THE TAPE|
|226 lbs.||Weight||640 lbs.|
|Flying dog||Pet||Flying goats|
|On the outside||Wears Underwear||Never|
THE PLAYERS: Norse god of thunder and prince of the fabled land of Asgard, Thor wields his enchanted hammer Mjolnir in order to protect his adopted homeland of Earth from the forces of evil!
Strange visitor from another planet with powers far beyond those of mortal men, Superman fights a never-ending battle for truth, justice and the American way!
THE BATTLE: To rid himself of his do-gooder stepbrother, Loki casts a spell that transports Thor from the golden streets of Asgard to the busy streets of Metropolis! The bewildered thunder god—his perceptions altered by Loki’s spell—attacks pedestrians thinking them to be trolls. Flying overhead, Superman sees Thor rampaging through his city, and flies straight into Thor at Mach 3, slamming the Avenger through the street and into the sewers below. Thor hurls Mjolnir at Superman who easily dodges it with his super-speed. The Man of Steel closes in on the blond powerhouse and pounds away at him in a flurry of super-fast, super-strong blows—thus playing right into Thor’s hands. Enchanted by Odin to always return to its owner’s hand, Mjolnir returns for Thor’s next volly. Dazed, Superman unleashes his heat vision, which Thor deflects with his hammer, but is distracted enough for Superman to fly in close and grapple with the thunder god in midair. Realizing he can’t overcome his opponent’s superior speed, the Asgardian calls down a massive lightning strike on them both. The lightning injures Thor, but being magical in nature, it pierces the Man of Steel’s invulnerability and puts him down for the count. Standing over the comatose Superman, the bloody and battered Thor proclaims: “Thou wert truly a worthy opponent—for a mortal!”
Of course, on paper though, it came out a completely different way. Back when Marvel and DC joint-published their long-awaited Avengers/JLA crossover, Kurt Busiek wrote the story so that Superman bested Thor in one-on-one, fair combat (though Superman said that Thor was the single toughest opponent he had ever faced).
Outrage! I loved reading Kurt Busiek's work on Marvels, Astro City and The Avengers prior to that, but after I had read that issue where Thor lost to Superman, I sort of lost respect for him and haven't read any stuff of his since (though not deliberately by choice...since he's a DC writer now, none of his stuff really interests me). Sif Superman can best Thor. Thor would make Supes cry like the girly-man that he is!