Martian Manhunter Vs Superman?!
Question: Who would when and why do you think so?
Answers: Who would when and why do you think so?
If we're going by basic powers then I'd say Superman would probably win.
Now, that time John had let loose some inner demon and didn't have his fear of fire, he slaughtered both Superman and the JLA but that isn't all the time.
I'll still say Superman.