Thor, Wolverine, and Hulk vs. Wonder Woman, Superman, and Batman
Rules: Featureless environment. No conveniently placed rocks cars or buildings. The characters know nothing of each other's strengths or weaknesses. (Thor would not know of Superman's weakness to magic.)
No exploitation weapons (Wolverine can't bring any Kryptonite, Batman can't pull a big magnet out of his ass.)
No environmental advantages. (fighting in space, no flinging anyone into space, or the sun.)
No friendly fire. (I know Thor, Hulk, and Wolverine hate each other, but they will have to fight as a team.)
No calling for help on either side.
For all purposes, adamantinum is unbreakable, as it has never been broken in any Marvel comics.
No pre-crisis Superman, or pre-crisis Superman feats. Wonder Woman cannot use the Atlas Gauntlets, Thor cannot use the Destroyer. Everyone is at their current comic book power level.