Good lord that is a tough one to answer - good question! I'd have to divide it by genre just to narrow down some of the prodigious talent on here. And some of those talents cross so many genres.
For that reason I'd have to decline a specific answer but, of the collaborations I've had the pleasure of, the following players have been an utter dream to play with (and I've probably forgotten many others!):
Bass: AlexJ, Haddock, Alby, BigMac, CKArmstrong, Jeebsie, DannyK, Carpenter, JMB65, Hingstler
Guitars: Tofzegrit, OliVBee, FrankieJ, Kennyadry, Ivax, Akethesnaker, PaulBOwens, PeterVeillon
Keys: Marceys, Liesching, Hurzel, Cody Tripp, woXey, Blind-Dog, JMRukkers, Piper
Sax: Wade, Fishinmissio, Lutz, Lionelher, cschlote, Pitt Brett
Other brass: Titi, Jaz100, sfiks
Vocals: Aleonz, Shi, Marmotte, Josh Dexter, JDF
A band made of any combination of those players would be an utter pleasure for me and I'm fortunate, in many cases, that I've collaborated with them.
I'd also happily invite DaFunkyDrummer to play instead of me. Just so I can watch and learn.