In terms of results, perhaps. 2011 was certainly a higher level. I'd also place Federer's 2005-06 on par with Novak's 2011.
Subjectively, 2017 was the most satisfying as a Federer fan. After the horrors of 2016, I was fully prepared for 2017 to be a lukewarm farewell year where Fed participated at the slams and his favourite Masters and ended the year in the 20-30 range before retiring. How wrong I was...
I say 2009, I was young and not really into tennis then, but I still remember Nadal-Verdasco and Nadal-Federer epics at AO, Soderling's famous RG upset, dramatic Wimbledon final and Delpo's heroic upset at USO. It was what first drew my attention to tennis, and first memories are always the sweetest.
2009. Even though Fed lost two dramatic slam finals it was still by far the most enjoyable year in the last 20 years. The depth of the field that year was incredible. Nadal insane AO win beating Fed in the final. Absolutely peak Verdasco at AO pushing Nadal to the limit - one of the best AO matches of all time. Murray peaking in masters 1000. Djokodal in Madrid - one of their best and most dramatic matches, very underrated. Soderling roasting dull at FO. Fed completing career slam in Paris then beating Pete’s record in London. Roddick’s resurgance during Wimbledon pushing Fed to the limit. Delpo’s USO incredible win beating back-to-back Nadal and Fed. Davydenko’s autumn and WTF. Many players peaked in 2009 only Djokovic was below par but he still won Paris.
2018, oddly enough.
Whilst 2011 and 2015 were his standout years, his comeback in the 2nd half of 2018 after injury and poor form was incredible to watch, esp after not winning a Slam for over 2 years.