All very fun, but Conker shaped my childhood.

Looks like I'll be in the minority, again. Tie between Conker and R&C for me. I played Conker on the N64 more than any Mario game (combined, and I've played a LOT of hours of Mario). I'm not suggesting I dislike Mario games, and they are quite fun for me, but Conker was a lot more enjoyable. Ratchet and Clank are high up there for me as a series. My favorite of any of the 3D platformers that spawned many sequels (Rayman is high on my list too). Banjo are Jak are great too. All have fine games under their belts.

Mario > Banjo > Conker > Ratchet > Jak

Mario is both the deity and patron saint of platformers 3D and 2D.

Banjo-Kazooie

I'd trade many of Nintendo's series for Banjo-Kazooie to be with Nintendo again.

Rare hasn't made another one.  They made Nuts & Bolts but havent made a 3rd one yet.  They did remake the 1st on XBLA with an HD pollish though.

Also, why no Crash Bandicoot!?

Short Answer: Microsoft bought Rare and basically killed the old Rare. Much of their people left and now Banjo (among others) is all but forgotten in Microsofts minds.

R&C, I enjoyed more titles of that series then of all the other ones.