Rafa is the clay king, no debate. Even Borg would have had trouble with Rafa. However, no other player is nearly as complete as Roger Federer. As a tennis purist, you cannot overlook the quality and efficiency of Fed’s movement and his level of proficiency on every stroke from every part of a tennis court. None of his shots, save his forehand, is the best in it’s class, but all of his shots are in the top 5 ever. His forehand is the single greatest weapon in the history of tennis, consistency, placement, and power all rolled into one.
Rafa has the clay thing solved, but benefited from other things like the slow down of the courts that happened in 2000 or thereabouts and continues to this day…as far as having the most impressive career grand slam, Agassi holds that distinction since when he won his slams, they were the most varied surfaces in the history of tennis (Laver had the same benefit as Nadal since 3 of the 4 majors were on grass during his tenure) so everyone was better at offense then just like everyone who’s successful now is good at defense (except Fed, who had to adapt his game and alter it to become more defensive at the start of his career–not easy to change your whole game and mentality after training that way your whole life). Nadal is the best defensive player, so he wins the most titles among those guys. Djokovic is second and Murray third. Fed’s offense is so good, he overcomes most defense, except Nadal’s and when they play on a truly fast surface (as fast as Roland Garros is slow), then Federer usually dominates. There are few courts like this left on the ATP Tour.
Winning Wimbledon is less amazing because the difference from the French is not as stark and the offensive players do not get much time to develop those skills since there are so few grass court events. There is not a single 1000 level grass court tournament, which is just plain ridiculous. Most of the season, even the offensive players like Tsonga have to play defensively because that’s what wins or you wind up having a career with somewhere around 6-12 titles (Tsonga has ten atp titles).