From my experience really nice creators are/were:
Ernie Chan (RiP)
Sergio Aragones (nicest guy in comics)
Mark Schultz
Mike Mignola (signs everything official Hellboy related)
Roy Thomas
Kelley Jones
George Perez
Steve Englehart
Jose Ladronn ("Final Incal")
Kevin O'Neal
Brian Bolland
Simon Bisley (a bit like a rock star, but cool)
Kevin Eastman
Colin Wilson
Adam Hughes (seems to be a nice guy, don't know about his wife though)
Eduardo Risso
A bit a strange are:
Neal Adams
($20.00 for a signature ? $10.00 for a photo?, seems to think he is the greatest)
Amanda Connor (comes of a bit arrogant, no sketching for fans at NYCC)