You're really making these hard, you know. Utilizing classic rock, scissors, paper deduction for this.
Iron Man is a product of modern engineering, scissors are a product of modern engineering..
Thor descends from Asgard at the top of the World Tree, Yggdrasil. Paper comes from trees. Scissors beat paper. Iron man wins.
Hulk SMASH (obviously). Usually he does so with heavy rocks. Rock beats scissors. Hulk beats Iron Man.
Black Widow is a defected Russian spy. I'm sure her naturalization process to the United States required lots of annoying paper work. Paper work is made of paper. Paper covers rock. Scarlett Johansson beats Hulk.
Captain America's shield is made out of adamantium. Adamantium is also used to make sharp things that slice and cut. Scissors slice and cut. Captain American beats Scarlett.
Hawkeye shoots a plethora of silly arrows and shit. I'm sure he's got some rock arrows in there somewhere too. Rock arrows beat scissors America.
And lastly, we have motherfucking Samuel L. Jackson. I don't think I have to explain.
Winner: Nick Fury
Oh wait, OTHER?? -- Galactus. Oh shit.
Winner: Still, Nick Fury. Whatever did you expect?
I'm a sucker for the Iron Man movies, and I'm woman enough (just enough) to admit that it isn't coincidentally linked to Robert Downey Jr.'s role as Tony Stark... Not in a creepy, "ZOMGRDJISSOSEXY!" way, so much as I adore his ability to convey dry wit. He's an excellent actor and (although pretty type-cast by that very dry wit) was pretty perfect for the character.
(That's my story and I'm sticking to it...)
Also yay Hulk, Thor, Captain America, and (hopefully) Avengers.