Front242 said:
That said, he obviously played extremely well at RG '08 too. If we're talking non clay I'd consider the third set of the US Open 2011 to be some of the highest level tennis ever exhibited by Nadal. And Djokovic too.
On average, Nadal's best clay court and grass court tennis was in 2008. On clay, it was the year where he found the perfect balance between aggression and defense (he was a little less aggressive on clay in previous years). Later on, he had to be more aggressive due to a decline in movement, which actually benefited his game in general, but made him slightly more beatable on clay.
On grass, his level at Queens and Wimbledon was amazing. Definitely the best sustained stretch of grass court tennis he's had in his entire career. Even the first week of Wimbledon was smooth. It's difficult to explain but just seeing him play, I knew he was going to win it that year. Confidence was obviously a huge factor too.
I think his serve got better on grass in 2010, but that year, it took him a little more time to find his footing.