Ok, so how would you build them?
Thor - big question. I'm actually tempted to go Ghost. He flies. He's practically immune to bullets due to armor, and he plows through barriers. His strike with mjolnier can be modeled as a blast. But let's be honest, none of the starting archetypes do justice to Thor (or the DC comics original version, Superman)
Hulk - Big Bruiser or Supernatural Creature. Hulk's abilities greatly exceed starting PC abilities, but if you want to "get to" hulk, I'd say start with big bruiser as the base archetype and acquire critter abilities on top of it. He's clearly got "Transformation," but his base tank abilities match better to BB.
Iron Man - this is the hardest one for me to pigeonhole. It makes me want Robin Laws to include a "flying brick" archetype just for Iron man, Superman, and Thor. I'm going to leave this one open, as I don't have a good idea how to do it. How would YOU build him?
Captain America - Masked avenger. He takes out massive numbers of mooks in every movie. To stay true to the movie character I would count his shield as a "gun" for schtick purposes.
Black Widow - oooh. Could be spy or thief. I'm going with Spy because the action scenes have her murderously effective at switching between all sorts of attack types, which fits the Spy archetype. Private Investigator might also work.
Hawkeye - archer, obviously
(Next movie set)
Falcon - cyborg, but you must completely switch his schtick choices. Take instead Personal Copter Rig, Interceptor Drone, Seeker Missile, Smokin!, and two other schticks that don't modify your body. GM's might consider allowing the last two to be gun schticks instead.
Vision - ghost? But switch out "love potion" for some other sorcery schtick.
Scarlet Witch - sorcerer
War Machine - use whatever you use for Iron Man
Black Panther - ninja or martial artist. Other stranger possibilities include masked avenger (but switch out guns for martial arts, and let him get Fu schticks instead of gun schticks), or possibly transformed dragon.
Loki - sorcerer. But go wild with scoring.
Winter Soldier - cyborg if you want to stay 'true to theme', though personally I think the starting archetype of gene freak matches the WS's demonstrated movie abilities better.
Thoughts? Disagreements? Better builds?