I think we need to restart this thread with a new poll since things have changed a bunch since the other one.
Here are the arguments:
Roger Federer
Age: 30
Resume:
16 Grand Slam Titles
Australian Open: 4 Titles
French Open: 1 Title
Wimbledon: 6 Titles
US Open: 5 Titles
Pros:
Without a doubt the most impressive resume of the three, he dominated for undoubtedly a longer period than the other two. He's probably the best player ever on grass and has no real weaknesses. For him, the titles speak for themselves. He is also better at 30 than the other two probably will be so his longevity has been somewhat freakish.
Cons:
The level of competition during his dominance was inferior to the level of competition the other two have faced. His main threats during the years he won most of his majors Lleyton Hewitt, Andy Roddick, Marat Safin, and a very young Rafa Nadal.
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Rafa Nadal
Age: 25
Resume:
10 Grand Slam titles
Australian Open: 1 Title
French Open: 6 Titles
Wimbledon: 2 Titles
US Open: 1 Title
1 Olympic Gold Medal
Pros:
The gap between Rafa on clay and anyone else is the biggest gap there is between any of these guys. Given that, it is logical to say that if you all all three players in their primes and simulated a bunch of tournaments on all three surfaces, Rafa would win the most since they're all close enough to split wins on grass and hard court, but Rafa would win a high % of the clay tournaments. His 2010 season was, at the time, arguably the best season ever. He holds a 17-8 head-to-head record vs. Federer, but they have been pretty even on clay. There primes didn't quite overlap but they have basically an even amount of matches of one in the prime and the other not since Fed played young Rafa and Rafa has played older Fed.
Cons:
Just how much weight do you put his clay domination? There is little doubt that Federer was better on grass and it certainly looks like Novak is better on hard court. Does this prohibit him from being called the best ever?
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Novak Djokovic
Age: 24
Resume
4 Grand Slam Titles
Australian Open: 2 Titles
French Open: 0 Titles
Wimbledon: 1 Title
US Open: 1 Title
Pros: In 2011, Novak just put up arguably the best year in the history of tennis. Putting up a record of 64-2 (with one loss being a retirement due to injury), Novak crushed fields that many consider to be the toughest ever. He was undefeated vs a 25-year-old on Nadal and beat him in the finals of both Wimbledon and the US Open. His only legitimate loss came to Roger Federer at the French Open. He's 24 and relatively healthy, so with Nadal showing signs that he may break down physically soon, and Fed entering his 30s, Novak may go on another dominant run.
Cons: He's only done it for one year. While he might be the best ever, you have to decide if he deserves being called that yet. He might keep dominating, but he also might not. This uncertainty goes against him. He's also never won the French Open, which will hurt his resume until he does. The main issue is whether or not you think one dominant year is enough or is it too likely to be a result of variance.
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There's a lot to consider here and I'd ask that you really look at the many angles before just voting based on total number of Grand Slam wins. You have to decide what it means to be the best ever. Do you value career accomplishments more than peak performance? Do you value level of competition or do you not want to punish someone when all they could do is beat who was in front of them?
I like to look at it simply as, "Which of these guys have been the best player I've ever seen?" That's just my interpretation of it though and I don't want to define best ever as different people are free to value things differently.