Who would win in a fight, Iron Man or Captain America?
If you want to stack stats, you have to go to Marvel's Power Grid.
Captain America is rated 3, or learned.
Iron Man is rated at 6, or super-genius. Level 7 is omniscient. Tony's intelligence is such that he can predict the future based on current trends.
Nod goes to Mr. Stark. Cap isn't smart enough.
Steve Rogers is rated as a 4, the peak of human ability. He can regularly lift 800 pounds. He's likely the strongest non-powered human who ever lived.
The Iron Man armor is rated 6, regularly lifting 100 TONS. Stark once knocked out the Hulk in one punch. Additionally, he can override the safety protocols to push his suits even harder. He once easily lifted a nuclear sub weighing 16,000 tons by overriding his suit's safeties.
Category goes to Tony. Cap isn't strong enough.
Cap gets a rating 2 here, normal... although normal is relative. Steve can sustain a jog at 30 mph, and can sprint at nearly twice that. For reference, a 3 rating caps out at 700 mph.
Stark in the open is FAST and gets a 5 rating. Supersonic. Even in close quarters, the suit is fast enough to outmaneuver Spider-Man.
In a race at least, Stark wins. Cap isn't fast enough.
Captain Rogers has a rating of 3. Enhanced. He has incredible stamina (he once sprinted five miles without being out of breath) and incredibly fast human healing.
Iron Man is rated 6 - superhuman. He has tanked nuclear warheads without even being concerned about the blast.
Iron Man wins by a longshot. Cap isn't tough enough.
Cap is rated 1 for having no energy projection. To be fair, however, his shield does give him some distance attacks.
Iron Man is rated 6. He's able to discharge multiple forms of energy, including making a sword and shield of pure energy, or even surrounding his already formidable suit with an energy shield.
Iron Man wins here, too. Cap doesn't have energy enough.
Steve Rogers is rated 6 here - master of several forms of combat. His reflexes border on superhuman. He is a master tactician, able improvise at a high level.
Tony Stark is rated 4 - experienced fighter. He, too, is a master tactician, although perhaps more on a larger scale rather than hand-to-hand combat. He does have awesome technology to assist him here, however.
Rogers wins this category in the end. Stark isn't the fighter Cap is.
Stark is faster, smarter, and more powerful in every conceivable way. Steve would have to incapacitate the armor, but he's not smart enough to come up with a way of doing this that hasn't already been anticipated and defended against. No offense to Steve, but punching Iron Man with his shield would be like me trying to suckerpunch a steamroller with a trash can lid.
Tony Stark wins, with one specific exception:
Unless it's a Captain America comic book.