Really, you shouldn't get this over SSF4. It's not as well balanced and missing the new fighters.
SSF4 is the far superior game. Unlike in the past generations, the newest edition isn't merely a slight improvement. It has bonus stages, extra characters, new special moves for everyone, and (for what it's worth) different cutscenes.
Oh, and the best reason to get it? It doesn't have that horrible, horrible "Indestructible" song.
Darn it, now it's stuck in my head again.