I don't know how you can compare the sales of the two games. They are very different in type. The only similarity is that they are both aiming at a more casual market.
With that said, I think Banjo will do better. The hard core crowd will support it and the casuals on 360 will welcome it... First, week might not be as high as LBP but it will stay higher over time.
LBP... I think will be another Viva Pinata... It will get great reviews but for some (fairly unknown reason), it won't get the sales I think a lot of people are expecting. First, week it will be high but really fall afterwards...







