If we were to poll people from around the world, posing this very question. Making sure EVERY demographic was fairly represented, using age, ethnicity, and regional location as criteria. I personally believe that logically, the consensus would be as follows, from top to bottom:
Spider-Man
Wolverine
The Hulk
Other results(no real specific order): Captain America, Iron Man, The Thing, Human Torch, Thor, Cyclops, Daredevil, Ghost Rider, Siver Surfer
Spidey's a no-brainer, and the only other big green guy known world-wide is Shrek, so... As for the OTHER guy, you can dress him up any way you like, but all he's gotta do is have those claws popped ,baby. People'll know it's the Wolverine!
I say this because of the movies, and all that it entails, media and marketing wise. They are so far reaching, much moreso than the comics, that's for sure. Forget theatre runs, think home video sales and rentals, pay-per-view, broadcast channels, and the list goes on. Then, as someone else mentioned, there's all the tie-in merchandise. So you'd be hard-pressed to argue the amount of exposure this medium ALONE brings these characters. Just SO MUCH! With that said, using the same theory, the most recognizable Marvel ladies would be, in order:
Storm
Phoenix
Rogue
Invisible Woman
Other results: She-Hulk, Elektra, Scarlet Witch, Spider-Woman, Ms. Marvel, The White Queen, Psylocke, Black Widow