On The Late Show, the episode with Chadwick Boseman, Stephen Colbert does a bit where little kids are supposed to come up with a TV show. One little kid is a Beatles nut and really knows his stuff!! Colbert gets in an geek fest “argument”with the kid which ends with Colbert saying that Revolver is the best Beatles album.
So there ya go. 
Most kids bought singles in the 60s because albums were just too expensive. $2.99 for stereo! It took the entire decade before buying albums became the norm. Early album sales are tiny compared with what came along later.
Yeah, and the kid says “Rubber Soul” and starts rattling off the songs on it… and he was a young’un. It was pretty cute.
And when Colbert aired the “completed” episode, the Beatles were Hugh Laurie, David Tennant, John Oliver and Michael Shannon. Fun!
I see that a case could be made for 1964 and/or 1967 for world beating zeitgeisty-ness but I’m going for 1966 because of Revolver.
Pepper had a nicer package and always seems to get the ‘popular’ vote, but it doesn’t have enough good songs. It wouldn’t make my top 5 of their albums. Penny Lane + Strawberry Fields might have swung it but I prefer Paperback Writer and Rain. So there.
If there was a year of their output I wouldn’t want to live without it would probably be 1965, but they were just bloody excellent at that point, not yet astonishingly innovating.