Hate to sound like such a Marvel fanboy but this "DC characters are more powerful/DC as a whole is more powerful" thing is complete crap! Who ever decided this? Thor is without question at the very LEAST on Superman's level.
The Avengers would have a definite shot in winning. The JLA could easily win too, but writing off The Avengers like so many have done is just silly.
Correct me if I'm wrong, but put The Scarlet Witch on Superman and he's out of the picture due to his weakness to magic. (Especially this "new" Wanda).
Put Thor on, oh take your pick, Green Lantern, Flash, any of the other hitters.
Conventional thinking would give Batman to Cap, but I'd give Batman to Ironman so Batman is out of the picture earlier (can't give him to much time to think).
Cap would be backing everyone up and calling the shots.
Again I'm not saying The Avengers WOULD win. But they easily COULD. And this is the generic version of the Avengers that I think most people remember (the team that actually met the JLA in the crossover). Nevermind factoring in Sentry who, at power-levels established by certain writers, might be able to tackle Superman and Green Lantern at the same time.