We are lucky to have had so many good players in one era (and good second string too with Murray etc) but (i admit my bias here) i still think Federer is the GOAT.
His style of play is just effortless and early on he was playing shots no one had ever dreamed of playing. He is a joy to watch. That is not to say that Nadal & Djokovic are not good players, they clearly are but their style of play is more brute force compared to Federer