I'm counting MSH vs SF and XvSFThis one right here is hard. If we just talking MvC and not the whole Vs collection, then I'll go with Tekken. Tekken has 7 core cames and 2 tag games. That's a much bigger impact than the 4 MvC games. Now if you included XvSF and MSHvSF in there too, it might have been closer.
I'm counting MSH vs SF and XvSF
Idk if children of the atom counts though