isabelle said:
Stanimal is a late bloomer, that's why he's not often injured, his body is still "fresh" for a guy of his age. Nalby was an early bloomer, he won USO junior at the age of 16, he played at a hight level much younger than Stanimal. he was only 23 when he won Masters in 2005. His body was damaged early, he had several surgeries before 30. You can't compare them because they didn't play their best tennis at the same age.
Interestingly enough, Stan has now played 589 matches to Nalbandian's 574.
While I agree that Stan is a late bloomer, he didn't exactly start that late - he played international events as a junior starting at 14 and turned pro in 2002 at age 17. He played tons of matches early on, so got similar wear and tear as Nalbandian.
But you're right that he's a late bloomer in that he didn't reach his peak level until 2013 at the earliest, when he was 28. Age-wise Stan's 2013 is Nalbandian's 2010, when he was trying to come back from a year and a half lay-off. The decline was steep from that point on - he finished #27 that year, #64 in 2011, #81 in 2012, and #228 in 2013. Stan, on the other hand, is still inching up - #8 in 2013, #5 in 2014 and is holding steady at #3 in the Race to London rankings.
All that said, while I do think that Stan is overall greater I think we have to be careful not to be too "Slam-o-centric." There are a lot of factors that go into winning a Slam. While it certainly is the most significant factor in determining greatness, perhaps along with the rankings, there are plenty of one-Slam wonders that are inferior players and with worse overall careers than some Slamless players. For instance, no one is going to call Marin Cilic greater than Ferrer, Berdych, and Tsonga. Maybe if Cilic has a strong five-year span, but as of now he looks like he caught lightning in a bottle.
Another classic example is Sergiy Bruguera, who is the definition of "clay court specialist." He won two French Opens and made it to another Final and a Semifinal, but was probably more like a #40-50 player on grass and hard courts.
Anyhow, I'm working on a study of Generation Federer (born 1979-83) and Generation Nadal-Djokovic (1984-88) and right now I have Nalbandian ranked #8 on the former and Stan #4 on the latter, although I'm still fiddling with the relatively complex system I've devised and not entirely happy with ranking Nalbandian behind Davydenko. Intuitively and by eyeballing their records I think Nalbandian was better. But even if I pushed Nalby up a rank, he'd still be behind Federer, Hewitt, Roddick, Safin, Ferrer, and Ferrero, whereas Stan is only behind Nadal, Djokovic, and Murray - I have him just ahead of Berdych, del Potro and Tsonga.