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.). But you won't find a player as gifted and elegant on court as him.

Nadal and Djokovic are more the working class, though they have lots of talent of course They are physically stronger, but this is not about talent, it can be learned/trained. I think Djokovic actually has tremendous numbers, because he had to deal with Nadal/Federer throughout his whole career and only in the last 2-3 years those two were fading a bit. But his style of play is not what I consider goat-ish, same goes for Nadal apart from clay.
And personality-wise Federer is above them as well, because he is such a likeable guy, well spoken and always a gentleman. Nadal is a very nice person, but kind of shy of course. Djokovic is just very fake imo and an attention whore.

My personal GOAT is Fernando Gonzalez though