It's an endless discussion. Rod Laver once commented that the pre-match meal of choice was usually steak and potatoes - stuff many pros would probable never touch today. Now they recover in ice baths, and hyperbaric chambers. No comparison.
I'm getting a bit sick of all the "greatest ever" talk. People think we're in some "Golden Era". Here's a list of reasons that, in my eyes, the accomplishments of Federer and Nadal are not as significant as people make them out to be.
Winning Roland Garros is easier now than it has ever been. Laver, when asked if Sampras had to win RG to be the greatest ever, said something like: "In my day there were about 5 clay specialists that I had to worry about. Now (in the 90's) there are about 50". IMO, that number is back to 5 again. It's mostly due the Spaniards and Argentines, who were once almost all clay specialists, and now (for the better imo) are much more all-court oriented.
Winning Wimbledon is easier than ever. The courts are slower, and again, there are no grass-court specialists. You don't even have to serve big or come to net anymore (which Borg did when he played on grass).
The two examples above make winning Roland Garros and Wimbledon back-to-back easier than ever - by far. It's no longer a huge adjustment to be made in 2 weeks. You can pretty much play the same way on either surface.
And last, but certainly not least: Tennis is just simply easier than ever - skill wise. Any good athlete can excel with the larger head frames and poly strings. The things the top guys do today was just impossible before. Sampras and Agassi could get about 2000 RPM on their groundstrokes. Djokovic averages around 3300, and Nadal has been clocked at around 5000. The margin of error that gives you is freaking HUGE. People thought graphite racquets were revolutionary, but I think it's nothing compared to the poly strings. Not only do the strings allow more spin, but it's been amplified by the type of racquet they allow players to use. Not very long ago, top players could have never gotten the control they needed with these frames - the poly unlocked their true potential. I'm confident that in the next 10 years, we're going to see players take things to an entirely new level - these will be the guys who grew up with this equipment. We're going to look back at today's players and realize they were not quite as spectacular as everyone thought.
I do believe that Federer and Nadal are two of the all time greats. Nadal may even be the greatest clay court player ever - I'm still undecided if he is that good on clay, or if he's just today's only true clay-court player. Djokovic still has to prove it to me - sorry, but a couple of good years doesn't make you an all-time great.
I think it's just a bit naive to start putting them ahead of the likes of Sampras, Borg, and Laver. Equal? Yes, but not better. Besides, how do we really know they're even that good - maybe everyone else is just that bad. Maybe they win so many Slams because they're that great, but it could also just be that no one else is good enough. There's a lot of great athletes in the game today, but I don't think there are many who have the mental and emotional toughness to play their best when it matters most (Murray, the top 3's closest rival, is a perfect example).
Rant over.