I don't know who the greatest male tennis player of all-time is but I may be the only person honest enough to admit that I don't know; prior to Rafael Nadal's convincing four set victory over Roger Federer in the French Open finals, commentator John McEnroe declared that Federer could cement his place as the greatest player of all-time by beating Nadal. McEnroe knows a lot about tennis but that is a ludicrous statement; discounting the not insignificant detail that the likelihood of Federer defeating Nadal anywhere--let alone on clay--is slim, why would one match totally define not just the Federer-Nadal rivalry but the totality of tennis history? With that French Open victory, Nadal now enjoys a 17-8 head to head advantage against Federer, including 7-2 in Grand Slam matches and 6-2 in Grand Slam finals. Any rational, objective observer would need to see Federer win nine straight matches against Nadal before seriously entertaining the notion that Federer is even as good as Nadal, let alone better than champions like Borg and Laver who did not suffer at the hands of their top rivals the way that Federer has been tortured by Nadal.
Martina Navratilova and Chris Evert enjoyed the greatest rivalry in tennis history; they each won 18 Grand Slam singles titles--clay court master Evert captured a record seven French Open titles, while grass court master Martina Navratilova claimed a record nine Wimbledon crowns--but few knowledgeable people would rank Evert equal with, let alone above, Navratilova mainly because Navratilova won the head to head series 43-37. Nadal has not yet matched Federer's total for career Grand Slam titles but Nadal is accumulating those laurels at a faster pace than any male player other than Borg and Nadal's mastery of Federer far exceeds Navratilova's edge over Evert. We will never see Federer play on equal footing against Borg or Laver, so comparisons of their careers involve making judgments about different eras, styles of play, equipment and so forth--but we have seen Nadal pummel Federer on multiple surfaces at numerous venues around the world for the past half dozen years. That accomplishment alone does not prove that Nadal is better than Borg or Laver but it gives a very strong indication that Nadal is better than Federer.