LittleBigPlanet is a game I never stop playing, while Super Mario Galaxy I felt to be the weakest 3D Mario. LBP is in my top five favorite games of all time, while SMG is far further down the list. I guess in that sense I'd go with LBP.
That being said, they're totally different styles of game. One is a 3D platform that focuses on some of the best single player level design around, while the other is a 2D platformer that emphasizes user generated content and messing around with your friends.
I've spent more time just screwing around in LBP, not even seriously playing the game, than I've spent playing all of SMG.







