It is hard to answer this question without touching upon politics, as that would be a significant factor. Either way, I'd probably choose the 70s. I find the late 60s to mid-70s to be one of the most fertile periods artistically, musically, and culturally. I love the mixing of genres, funk, some prog rock, etc, as well as New Hollywood film, New Wave sf and Ace SF classics, the blossoming of fantasy fiction during the Ballantine Adult Fantasy run (1969-74) and the Daw line, and of course D&D in 1974.
There was a sense of hope in the 70s. The cultural revolutions of the 60s, the end of the Vietnam war, and a still thriving American economy and middle class. Yes, there was the hanging cloud of the Cold War, but a higher percentage of Americans could live some semblance or version of the "American Dream."
Or to put an image to it: