We all know that every one of them here could essentially win. However...
Captain Marvel I think spends forever fighting Superman and Wonder Woman. Technically speaking, I think Wonder Woman and Captain Marvel would be a stalemate, since she doesn't have the magic weakness. GL could take down Superman, after he takes down J'onn. I think Flash would play it really, really smart, and zip around so fast that he dodges everyone's attacks until they're worn out. IMP and he wins.
I'm giving this to Flash. If not Flash, then destructively I think GL or Superman would win...but I think Flash has got this down.