It can't be Wolverine, his movie rights are owned by Fox and I don't see Marvel pushing an X-Men character too much even if it's Logan
.
I would say Spidey hands down if it weren't for the fact that his movies aren't doing too well...then again, he does have a cartoon going on that from a Marvel standpoint has been a success. And his video games have, for the most part, done well.
The only other ones I could think of would be between Cap and Iron Man...but the latter is still inverted, and a lot different from MCU Tony, and I think the former would fit a lot more easily, especially with how well Winter Soldier did.
And I'm with Hyperstyle in wanting more Power Pack
.