If you never play SMB I think that is the best option for you. The single player rocks, you never get tired trying to lead the monkey to the goal. And now the game includes a lot of mini games.
Anyway i will be buying Rayman in couple of weeks, i'm a very fan of the series and the bunnies looks great and fun, Rayman has a lot of fun within the game.
I have to admit that is a very difficult decision.