I'm personally more partial to the original Marvel versus Capcom, especially for its stylistic purposes, eg; the music and backgrounds; those two things I wasn't all that big on with MVC2.
true, the original MvC was a more technical and tight game but I can't help but love the sheer carnage that MvC2 brought to the table. I also hope that Capcom takes the time to work out some of the balance issues with some of the characters before the release.