For me this would be Federer, but not because of any numbers. He just is the most talented one to ever walk on a tennis court. Watching him play, it felt so effortless what he was doing and he basically had no weaknesses and could do it all (forehand, one-handed backhand, net play, good/precise serve, effective slice) on any surface. His sheer numbers are surely a bit inflated, because he was in a league of his own until Nadal was more competitive on hard/grass and Djokovic showed up on the Tour - the era when Fed started to peak was rather weak looking back (Roddick, Hewitt, Safin, Nalbandian, Davydenko etc.).
When you think about it, numbers of all 3 of them are a little bit inflated compare to some previous generations due fact that there is no big difference as before in terms of surfaces. Back in the 80s and 90s it was a huge difference to play on grass or let's say hard surface.They slowered some of them, like grass and by doing that it was possible for even Nadal to win Wimbledon.
Djokovic is just very fake imo and an attention whore.
Djokovic is trying to hard to be liked, and that never works. He just doesn't have charisma, and you can't learn that,either you have it or not.But its also true that when you looks he leads in head to head vs both Nadal and Fererer,and that could also be argument for some that he is GOAT.
Reaarding the question, even if Djokovic or Nadal surpass Federer in terms of grand slam wins, for me he will stay the GOAT. But my favorite player is Pete Sampras.