Now to attempt to give you a reasonable answer; the team that comes to mind that could best challenge them (and some extreme circimstance would have to exist to cause them to team up) would be:
Cyborg Superman
Superman
Gladiator
Out of 10 fights, I dont see either team winning every single time; I think this would be close in all honesty...
I dare say either a 5/5 split or 6/4 in favor of Marvel's finest.
Black lantern firestorm
Hal Jordan green lantern
Stardust
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."
I originally had this exact list then I decided to swap out genus for firestorm just for potential. :-P
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."