The best song of the 1960s. Well, it would have to be from Lennon and McCartney of course. It is subjective.
My vote would be HELP. Not only for our special decade, but for our Century. This version, the first time the Beatles played it live on stage, John messes up the lyrics you will notice, on second verse he just makes fill in noises as he forgot his own song. No matter, these guys are the best ever, the very best of their time and all times. They are and were so many, many, light years ahead of earth, one can not even speak of the matter.