Ugh. I'm beginning to dislike these "All-Time" lists. There is never going to be consensus, and while i love the fact that these lists do bring history and the present closer than perhaps they might be in people's mind, there's really no way to compare the accomplishments of the past with those of the present.
The caliber of competition, the accesibility of what was historically an 'elite' sport, the number of worldwide events, the variation in court surfaces, the elevation of physical standards for athletes, the 'improvements' in the technology that surrounds the game, the era of 'Open' tennis competition, the ability to travel more easily are all reasons for us to be incapable of truly comparing, 'once and for all,' the greatest players of tennis in any meaningful sort of way.
In the last 2 decades, there are a handful of players whose games themselves can truly illustrate how brilliant tennis can be. The all-court game is, to my mind, the best indication of a players 'overall' historical standing. Their career statistics are important without question; champions are champions because of the number of majors they've won and the circumstances under which they've been able to produce their very best. But from a 'purist' standpoint, a player's ability to serve, return, hit groundstrokes, hit volley, attack and counterpunch are perhaps better ways of establishing their place in tennis history.
John McEnroe never considered himself to be a 'pure' serve&volley player; Connors never thought of himself as just a baseliner; Fed and Pete are classic all-courters (though perhaps Roger epitomizes this moreso); "Big Bill" goes down as one of the first huge serves in tennis, but what about the rest of his game? (seriously...i'm asking!) What about all of the other 'greats' who contributed to the game in some way or another? How do you end up rating them against one another? Apples and oranges!
So what if we look at players for their overall ability on a court, not just their records, and not just their one 'particular' contribution to the game? Who wins then?