I've always disliked trying to anoint a sole GOAT. It seems like an exercise in futility for the most part, considering how much basketball has changed.
I prefer to do it by decade:
50s: Bob Pettit
60s: Bill and Wilt
70s: Kareem
80s: Bird & Magic
90s: Jordan
00s: TD & Kobe
10s: LeBron
20s: TBA
These guys are guys that I think would be successful in any era, and have had remarkable impacts on the game. Their ability and work ethic would translate to any era.
Bill is as good as any, and has an argument to the be the top.