Who had/has more members- Justice league or Avengers?
And, setting aside such things as Squirrel Girl, who would win?
Use Flash, Superman, Martian Manhunter and Green Lantern to their full abilities and they win IMHO.
Don’t eff around though. Knock Scarlet Witch out first. Supes beats Thor (according to Busiek) have MM take out The Sentry (He may be the only JLA member who can do so.) Have Flash take out Dr. Strange before he can wreck everyones day.
This is a perennial debate among comic book geeks. It’s always struck me as being silly (I don’t think esoteric comic book debates are silly per se, I just think this particular one is).
Heroes in the Marvel Universe and in the DC Universe just exist at very different power levels. The comics aren’t terribly consistent, of course, but dating back to the attempt to seriously codify power levels in the 1980s with Marvel’s Official Handbook of the Marvel Universe and DC’s Who’s Who: The Definitive Directory of the DC Universe, the strongest heroes in the MU can lift in excess of 100 tons. The strongest heroes in the DCU can lift tens of thousands of tons.
Captain America vs. Batman? That’s a debatable outcome.
Superman vs. Thor? It’s not even close. Thor does have magic, against which Superman’s invulnerability isn’t fully effective, but one full-strength, full-speed punch from Superman and Thor becomes a red smear.
I’m curious. How? Full immediate regeneration is hard to beat.
I remember a JLA/Avengers crossover way back when. There was one part where Superman confronted the Hulk while he was going berserk. Superman let Hulk beat on him and transferred the kinetic energy through his body down to the Earth’s core or something. Hulk eventually got bored and left.
Telepathic attack, I presume.
I’ll set aside Squirrel Girl when you set aside Superman. 
The win would go to the Avengers, of course.
Well, it does look that the Spectre had a Justice League affiliation at one point. So the rest of the JLA could go out to a bar. The Spectre would join them five minutes later.
The Spectre’s power waxes and wanes a great deal.
http://www.geocities.ws/cheeksilver/jlavsavengers.htm
The above link is the definitive argument about JLA vs. Avengers, as told by Silver Age comic book writer Unca Cheeks. Enjoy.
That’s true, but the Justice League also has the Phantom Stranger. And Dr. Fate. If just one of those three is currently wielding god-like reality manipulation powers, it’s still the Justice League in a cake-walk.
The only chance the Avengers have is if the Scarlet Witch is currently also at her maximum depicted reality manipulation powers. But at that point, she’d also be insane, and would just create a reality where everyone was a puppet, or something, so she’d at best force a draw as the Avengers and Justice League have to team up to set reality right again.
I like it!
What would really happen (sorry, Unca Cheeks!) is that Superman would see Captain America and immediately halt all offensive actions by the JLA until Mr. Truth, Justice and the American Way got things sorted out. I think Diana would react the same way, using the lasso to suss out the Truth. 10 minutes after they meet, the combined group is off to kick the ass of whoever set them up.