Humblebrag, I busted both Negreanu and Greenstein at the same HORSE event a couple of years back (beat: still didn't cash).
Greenstein was quiet but very friendly to everyone the whole time. Didn't get a book though
Renegs on the other hand would play it up and be super friendly for the cameras and to any moderately attractive female nearby. If cameras were gone, or you weren't some known commodity, complete opposite. He has a very fragile ego.
Raymer is very friendly at mix games, played with him several times and always good table talk.
And for someone less famous, I'll throw Scott Davies out there as probably the nicest person I've ever played with at a poker table. He's a good friend, but never seen him say a mean word to anyone.