The simple answer is there isn't a best one. There's some shit ones though.. What Goes On, Yellow Submarine, ObladiOblada, Revolution Number 9 to name but 4. Still leaves over 200 classics though! :)
I've been listening to the early stuff recently and I have to say that With the Beatles is my fave album at the mo. Next month it'll probably be Abbey Road though - that's the way it works with the Beatles.
ps. Interesting fact. My dad's uncle Ernie used to live in John Lennon's house 251 Menlove Avenue, Woolton.