I'd think...probably...I'm going for the following based on abilities, with heavy refluffing in several cases. Just going off of the basic cinematic universe characters...
Captain America: Valor Bard (sans the singing, of course. But inspiration point doling oration all the damned time).
Iron Man: Ancients Paladin (He certainly knows how to use "the light." plus lots of smitey pew pew spells)
Thor: Tempest Cleric...with a Dwarven Thrower Hammer.
Black Widow: Assassin Rogue.
Hawkeye: Hunter Ranger. (maybe some leeway on his ranger spell choice selection to duplicate special arrows)
Hulk: Berserker Barbarian.
Falcon: Champion Fighter w/ Wings of Flying.
Scarlet Witch: Wild Sorcerer
Vision: ...I'm going with some kind of Mystic
Antman: Wildshape Druid w/ special specific (smaller or larger) shapechanging and all animal-related spells (speaking, control, etc...) apply only to ants.
...and while I don't really consider either of them "Avengers" though I'm sure both have at least honorary membership and they've worked together many times, bonus heroes:
Dr. Strange: Abjuration Wizard
Spiderman: some kinda Monk for all of the flippy fighting stuff, ki points can handle/cover the special powers.