It seems irrefutabel to me that the 1970's to early 80's was the best and most competative era in pro tennis history; and Bjorn Borg dominated it. Sampras may be a close second, but he did not face the consistent level of competition that Borg did. Consider Borg's overall record in light of the fact that he 1)opted out of the Australian Open, 2)never won a US Open,and 3)retired at the very young age of 26. Yet his record at Wimbledon remains second only to Sampras, and his French Open record still stands- more than a quarter century later. In my opinion, his accomplishments alone make him the best player ever. Combine this with what likely would have been, had he not walked away from the game, and he remains in a class by himself.
Update: In response to san1702's post...First, it is true that Borg never won the US. He did however prove his proficiency there, playing four times in the championship. Contrast that with Sampras and the French Open- Sampras never even made it to the final. Lendl never won on grass, on the list goes. As to McEnroe, he and Borg were 7-7 in majors when Borg retired; but Borg had a winning record against him in all matches. So that does not hold water either.
Update 2: Today Roger Federer tied Borg's record of 5 straight Wimbledon Championships. Had Nadal won, he would have accomplished the "impossible"- he would have won the French Open and Wimbledon back-to-back. No one has done this besides Borg, and he did it three years in a row (1978-1980). Further proof that Borg is the best ever.
