Classic Titans v. The Fantastic Four
Cyborg
Raven
Changeling/Beast Boy
Starfire
v.
Mr. Fantastic
Invisible Woman
The Thing
Human Torch
Setting:
Any large, open chamber, about the size of a gymnasium. For simplicity's sake, let's say the walls and ceilings are unbreakable and all entrances/exits sealed. The ground is just plain old concrete, very smashable.
Battle Conditions:
Both teams begin about, say... 300 ft. apart (opposite ends of the gymansium). No one is allowed weaponry (excepting integral weapon systems, in Vic Stone's case). Everyone acts in-character.
Which team wins? Personally, my money's on the Titans. While both groups have excellent teamwork, I think the Titans match or slightly edge out the FF in power. Cyborg and Starfire can counter their opposites (Thing and Human Torch, respectively) while Raven could bypass Sue's forcefields with her teleportation.