Answering this question from an emotional and "this is more Nintendo than not" point of view rather than a business point of view:
Banjo-Kazooie: A few of Rare's IP's would be welcome back into the Nintendo family, but I feel that this one would work better than Conker, Killer Instinct, and Perfect Dark. Banjo-Kazooie is indeed another kid-friendly platforming series, but I feel its unique blend of 3D open-ended collectathons would complement Nintendo's other games well. The 3D Super Mario games have largely gone in other directions since Sunshine, so this style of games would not overlap that much with existing Nintendo series. The dynamics between the major characters work well enough even in gibberish to give the games their own personality distinct from Nintendo's existing series. We'd also get a good candidate for Smash Bros. And besides, the two main games and the non-Nuts-and-Bolts spinoffs were Nintendo exclusives anyway, so unlike with series like Castlevania, there wouldn't be much in the way of depriving fans of other platforms.
Honorable Mentions: Professor Layton, Mega Man, and anything popular on the NES or SNES that has become disused ever since.
Love and tolerate.
