It's either Flash, Supes or Wonder Woman.
They would all dispose of Iron Man, Cap, Spidey, Robin, GL, Wolvie and Iron Man fairly easily.
The wild card is how each of them would do against prep time Batman.
If Batman actually wanted to kill someone but knew he'd have to face a meta-human, he'd do it in a subtle but nasty way, like with poison or a virus. And I don't know what anybody could do about that.
I guess I'll go with Grant Morrison's Superman, he'll just resurrect me with the miracle machine in his head or he'll sing the song of reality at the end of the universe while stabbing a story vampire or some shit.