wouldn't match up with Hulk; he'd match up with Thor, who would instantly overpower anyone else in the JLA, and he'd be lucky to get a tie. (Thor is a lot
more powerful in the comic books than he is in the movies, and he's magical, which would give
a big problem.)
Batman and Captain America are as evenly matched as any two are, and so basically negate each other. Flash would not beat Iron Man very easily but I could see him winning eventually, but then you've got Hulk vs. Wonder Woman. Either way, there's still the Green Lantern problem, so yeah. Poor, poor, tiny insect-themed Avengers.
And Martian Manhunter's not in the JLA right now. He would make a big difference, but if you open it up to past (or future) members, then it just gets a lot messier.
I can't believe I'm arguing this. Hello again, teenage years, how've you been?