I own/owned all 3 and i'd say MKWii
Mario Kart:
Good single player ...great fun online ...if you've played other MK games then you'll know what to expect !
SSBB
Personally I hate this game ...but loads of people love it so don't take my word for it. I found the controls and gameplay awfull and the whole game generally boring. Also it seemedvdifficult finding opponents online.
Galaxy
Brilliant game ...you can't go wrong with it really . No online or (real) multiplayer but as a single player game it's extremely satisfying and will "wow" you on many occasions.
To sum up , the reason i'd go with MKWii is that i'm competetive and enjoy playing against my Wiitalk buds so if you're not that competetive and enjoy good single player games go with SMG
