Verified answer

That's a tough one. Thor would win not very easily. Thor Electricity and weather manipulation, Thor would blast Superman and after that wound Clark with Stormbreaker.

Superman

I think Superman, but only by a hair. Since he's vulnerable to magic, a hit from Mjolnir or Stormbreaker would hurt him.

Thor would win on a planet that had a red Sun.

Anywhere else, it would depend who hit first. If my knowledge is correct.

Superman is vulnerable to magic and since Thor's power is considered magical, Thor would win if he hit first.

Superman is incredibly fast so if he hit first, his strength and speed would win out.