Federer and Aggassi are the only ones who have won all 4 slams on the current 4 different surfaces. And Federer has won them all (except the French) more than once. I think that is phenomenal and that record will probably stand for a long time. I really liked Pete and he is up there too, but if you go by the record books, Roger has it in the bag.
Plus he makes the phrase “poetry in motion” come alive. I have never seen anyone including Pete move around the court as gracefully and effortlessly as Roger.