Fair argument. I think both of them had to play Nadal who was playing at a high level, but I can see why you chose Federer, since Fed in his prime never exactly played a "bad" version of Rafa, since Rafa at least at clay locked up earlier in his career, whereas, 2015-16 nadal was terrible everywhere. On clay, I say its about even since both of them took several beatings on the dirt vs Rafa, but Nole definitely played him wayyyyyyyy better than Fed did (hence, Nole was much more of a proper "rival' to Rafa on clay than Fed was). On grass, Fed definitely played a better version of Nadal, especially in 2007/08. Also, Nadal and Nole's grass peaks never exactly co-existed tbh, unlike Fed and rafa, who played each other thrice between 2006-08. IMO Nole's grass peak was during 2014-15 (he played amazing in 2011 too, but the insane amount of momentum he gathered from the first six months of the year basically willed him to the title). On hard, I'll go with Nole. Nadal was unhuman in AO '09 where Fed played him, but a lot of the times where Rafa had to fight for a high-profiled HC tourney he had Djoko in his way, and not Fed; including the Olympics, US Open (3x), AO (2012), several other masters, WTF, etc. Additionally, by the time Rafa was a consistent threat and even occasional favourite depending on his form on a HC, it was around mid 2008-early 2014, where Nole was now his biggest rival. I see your arguments, but its still so even since surface-by-surface; they both had to deal with an amazing nadal on clay, while Fed had a better Rafa on grass and Nole had a tougher Rafa on hard.