Re: Superman vs. Captain Marvel
Everybody knows CapMarvel's story: he was a copy of Superman, created after the success of the Man Of Steel, an then he became even more famous than DC's hero, selling even more comics duriing the 40s.
Then the comic sales started to be worse in general, and DC sued or threatened to sue Fawcett Comics, and Cap's comics disappeared. DC ultimately bought the rights for this character and for many others to add them to their own fictional universe, but once there Superman is the main DC character, even over Batman I would dare to say, Superman started it all, and DC can't allow that his main character is easily beaten by his clone/copycat, that's why you'll find several fights between them where Superman always wins (like the one above posted by CapStacy), because Superman is a bigger interest for DC than CapMarvel, so the writers will mostly write accordingly.
They have basically the same powers with similar levels, because one was created to be a copy of the other. CapMarvel has magic, ok, but Superman's weakness to magic has always been lame and silly imo, magic should affect him the same way it affects everybody else, but counting with his invulnerability, so a magic lighting would hurt him just the same way a natural one would if the magic one has the same level of power, magic would just be another kind of energy. CapMarvel's main weakness would be that he is actually a kid, but sometimes this has been used to make him look more naive and plain dumb, when he actually has the wisdom of Solomon, and even if in modern incarnations he has kept some of his childish personality when he is the Cap, he should be mostly shown as a hero as intelligent and wise as Supes.
So in my opinion a fight between them should be mostly a tie and their powers should be very similarly leveled. If Superman should be stopped, CapMarvel should be one of the first heroes to call, and the same thing the other way around. The writer would have the last word about who should win (85% of the tmes will be Superman, but not necessarily because he is stronger, the point of my whole post, DC and the writers and the readers just like Superman more because he is more popular, so he will win most of the times, he was "the first superhero" and kind of deserves it), but the fight should be shown as a balanced one if both heroes are at their best (not being mind controlled or weakened by other factors).