1966, Revolver is written (at least much of it) and recorded. The Beatles do their last tour. John writes Strawberry Fields while making How I Won the War movie. Paul presumably writes Penny Lane soon after.
John says Beatles are more popular than Jesus (and for that year and the next, was probably right).
Paperback Writer/Rain and Nowhere Man/What Goes On are released as singles.
Beatles are at the top of their synergy in the studio. John can toss off "And Your Bird Can Sing" and George can make it into a masterpiece. Experimentation abounds--from backward recording to innovative use of drum loops and close-miking of horns.
Yesterday and Today is released with Butcher Cover, which causes even more publicity--the album of songs nipped off the British albums includes a number of classics.
Beatles begin recording Sgt. Pepper in November.
It was really an amazing year--plus Pet Sounds, Sunshine Superman, Younger than Yesterday and Blonde on Blonde were released--even if they weren't by the Beatles, they were all still pretty damned amazing.
I go for 1966 as the greatest year for pop music because I think 1967 is a little bit hyped (although the Summer of Love produced the Doors first album, Surrealistic Pillow, Disraeli Gears and Love's Forever Changes as well as Sgt. Pepper).
I think the wave crested in '66 and broke in '67.