Stark/Banner vs. Rogers/Thor
In the scene in AoU in Stark tower, right after the team first encounters and defeats Ultron, let's pretend that the argument between the Avengers developed into a full blown fight. Tony and Banner teaming up due to both of them developing Ultron, Cap and Thor teaming up as they're the ones who were most strongly opposed to Ultron's creation. Let's further pretend that they're so pissed off that they're willing to kill the other team as they feel that the other team is a threat to world peace and security.
Scenario 1: The fight erupts right in the middle of their heated debate, meaning Tony is not in armor, Steve doesn't have his shield though it is within the room, Banner is still in human form, Mjolnir is on the table. The rest of the avengers quickly vacate the building as the fight erupts. Who wins?
Scenario 2: All the combatants are allowed 5 mins. to arm themselves while the other Avengers vacate the premises. Fight is still in Stark tower. Morals still off.
Scenario 3: The other Avengers manage to break up the fight. The combatants agree to meet again in 1 week in an honorable fight to the death. Tony and Banner stay in Stark tower and have all of Stark's resources to prepare for the fight. Thor flies Cap to Asgard and has all of Asgard's resources to prepare for the fight. Despite having prep time, the combatants are only allowed to bring their standard weaponry to the fight - no extra equipment or enhancements allowed. Stark and Banner obviously have way more IQ but Steve and Thor have more tactical and battle knowledge/experience. Who wins?