Glad someone finally asked. 'Yesterday' is my all time favorite. And whenever Im reminded of it, it starts playing in my head. It is such a beautiful song.
I looked through the entire catalog of more than 250 Beatles songs, and it is almost impossible to pick a favorite -- there are just so many indelible personal and cultural memories tied up in them. But if forced to pick two (just can't bring myself to pick one), I would have to agree with Ryann Movie Lover: Yesterday and Hey Jude.