They're so different it's difficult to say which is "better" for your particular circumstances.
Which genre do you tend to play more: fighting games or old-school classics like Pac-Man, DK, etc.?
When you position the cab, how visible will the sideart be?
How about lighting? Other gameroom decor?
Consider doing a modified Benjamin Franklin
Pro & Con list with "Marvel Pros" in one column, "Marvel Cons" in the next, "Classic Pros" in the third and "Classic Cons" in the last.
If one "Marvel Con" balances out two "Marvel Pros", cross all three out.
(same art, different category)
If a "Marvel Pro" balances out a "Classic Pro", cross them both out.
(different art, same category)
Repeat until you have your answer or an idea you like more.
Scott