In all honesty it depends on the suit.
Mk 1: not a chance
Mk 2: Maybe...
Mk 3: He could put up a good fight
Mk 4-6: Yeah, he could put MegaMan down
Mk 7-11: It would be a very good battle
mk 12: The cloaking power would give Stark a very great advantage
Mk 13-14: the advanced titanuim armor would be a very dramatic defense
Mk 15: The stealth setting would be terrific
There are several more, but I made my point