The only years Nadal has been competitive on serve with this year are 2010 and 2013 on hard courts. Claydal2017 right up there with 2012 and 2008 versions. Combine his both 2017 clay and hard performances plus the impending end of year run and it will be his best year if we ignore grass.
Federer is similarly excellent, but if his back dogs him the rest of the year this would just be like a prime year, not a "peak" year (2004-2007). At this point Fed would have to decisively sweep his remaining events to even think of peak at this point. He had the potential to hit that over this hard court season, but went belly up at the last gasp.
Most of the "experts" on TTW look at movement alone and of course these two moved better when they were younger (age 23-24), but the game has become much more about power and better developed serving plus more. Most of these things don't reveal themselves until you look at the stats. Nadal on clay this year was insane; 57% 2nd serve points won for career, but 2017 was 65% and a whopping 75% at RG.


That is crazy stuff and bodes very well for Nadal's longevity as unlike most veterans his serve had been falling apart late in his career. The reversal in his serve numbers in 2017 is nothing short of stunning. The TTW arm chair "experts" are by in large oblivious to this and get their rocks off watching long neutral rallies or something.