SSBB will definitely sell better (a lot more)...but DMC4 will definitely have a great week.
DMC4 will be popular and sell well, but it is NOT a Final Fantasy XIII or Gran Turismo...
Eitherway, though, I expect DMC4 to sell 150,000+ copies which is very respectful for the small install base of ps3's and 360's...
PSN ID: Sorrow880
Gamertag: Sorrow80
Wii #: 8132 1076 3416 7450