I would have to say Iron Man 2 cuz those metal costumes rocked. Forget the spandex superheroes in walks steel.
(except for Black Widow she can wear spandex :)
G.I. Joe had cool gear too. Mech suits and ninja outifits, what a great combo.
Ohh yeah and dont forget Pan's Labrenth truely awesome costumes there.
I'll stop now . . .