I would almost nominate “Nights In White Satin” for a top spot because it bridged musical elements of the early 60s with the late 60s. Sinatra or Nate King Cole could have crooned it and the Beatles could have mixed and orchestrated it. Its contemplative moodiness, dynamics, bridge, and romance captured the feelings of that entire decade.
Days of Future Passed on a reel to reel was better than just “Nights in White Satin.”