In most sports it is difficult to single out who is the best player of all-time but it is generally somewhat easier to determine who is the best player at any given time--and right now Rafael Nadal is clearly the best tennis player in the world.
Nadal's convincing Wimbledon victory is a landmark event in Open Era history. Nadal now owns a Secretariat-like 3840 point lead over number two ranked Novak Djokovic, while Roger Federer has dropped to number three, his lowest ranking since November 2003. Nadal's Wimbledon triumph is his eighth career Grand Slam singles title, making him the second youngest player in the Open Era to win that many majors; the prodigious Bjorn Borg was just 23 years, 31 days old when he reached that milestone, exactly one year younger than Nadal was on Sunday when he blew away Tomas Berdych in straight sets in the Wimbledon Finals. Nadal has dominated the ATP Tour this year with a 47-5 match record while winning five events; he was similarly dominant in 2008 and the early portion of 2009--winning three out of four Grand Slams at one point, including the tough French Open/Wimbledon double--before injuries slowed him down and enabled Federer to also pull off a French Open/Wimbledon double to reclaim the number one ranking. Borg remains the only player in tennis history to accomplish the French Open/Wimbledon double three times and he did it consecutively (1978-80), arguably the most difficult feat in the history of the sport.
Nadal is now tied for seventh on the all-time Grand Slam singles title list, matching Fred Perry, Ken Rosewall, Jimmy Connors, Ivan Lendl and Andre Agassi; two more wins will enable Nadal to tie Bill Tilden for sixth on the list and one more win after that would match the 11 Grand Slam wins tallied by Rod Laver and Borg. If Nadal wins the U.S. Open he will become just the fourth player to complete a career Grand Slam in the Open Era, joining Laver, Agassi and Federer.
When Federer was Nadal's age he had won six Grand Slam singles titles, so Nadal is significantly ahead of the pace established by the player who many people have proclaimed to be the greatest tennis player of the Open Era. I have repeatedly said that these pundits prematurely crowned Federer; in a 2008 post titled Fantastic Four: Nadal Matches Borg's French Open Streak I wrote:
For quite some time, people have been trying to anoint Federer as the greatest tennis player of all-time but despite his impressive accomplishments it makes no sense to confer that title on him when it is not even certain that he will be considered the best player of the current era: his main rival Nadal owns an 11-6 head to head record against him and has come much closer to beating him on the grass at Wimbledon than Federer has come to defeating him on the clay at the French Open. Considering that Nadal is almost five years younger than Federer it is entirely possible that he will eclipse what Federer has done; after all, five years ago Federer had just won his first Grand Slam, while Nadal already owns four Grand Slam titles, beating Federer along the way each time.
Then, in a 2009 post titled Debunking Myths about Bjorn Borg, John McEnroe and Roger Federer, I declared:
Wilt Chamberlain once said that if he had thought that anyone was going to break his all-time NBA career scoring record then he would have put it "way out of sight." If Borg had been interested in setting the career Grand Slam record, then he would have annually journeyed down to Australia and most likely dominated that event the way that he dominated Wimbledon and the French Open--and he certainly would not have skipped the 1982 French Open when a victory there would have tied Roy Emerson's then record total of 12 Grand Slams (six of which were Australian Open titles won by the amateur Australian player between 1961 and 1967; professional players were banned from playing in any of the Slams until the start of the Open Era in 1968).
Nadal has consistently dominated Federer head to head, owning a 14-7 advantage, and after Nadal's 2008 Wimbledon win it was clear that Nadal had surpassed Federer as an all-around player; if injuries had not hobbled Nadal during 2009 then Federer would likely only enjoy a 14-10 lead over Nadal in career Grand Slam singles titles instead of his current 16-8 margin--but even as things stand now Nadal has a very realistic chance of approaching Federer's record.
I will not make the mistake of prematurely crowning Nadal the way that some people foolishly prematurely elevated Federer; all that can reasonably and objectively be said right now with both Federer and Nadal still actively playing is that the short list of greatest Open Era tennis players must include Borg, Pete Sampras, Federer and Nadal.