Iron Man vs. Superman
We all agree - or should - that Superman gets the majority on Tony. But how hard does Tony make him work for it?
1st Scenario: Current Iron Man vs. Current Superman. Both characters are in their typical mindsets/personality. Neither character has any information on the other and the battle takes place in a populated New York City.
2nd Scenario: Iron Man vs. Superman. Both characters can draw upon their entire history of feats so long as they're canon. Both characters have common knowledge of the other.
3rd Scenario: Iron Man has access to any and all his armors he's ever used and gets 24 hours prep to devise a plan/attack method to beat Superman, barring high end artifacts such as the Infinity Gems. Superman is aware of the depth of Iron Man's intellect and resources, but does not actively prepare to face him.