'She's so Heavy' off Abbey Road (you should have heard me and my sister do the dishes to that album when we were younger - the neighbours must have thought we were murdering each other!)
Best is very subjective as there were so many styles adopted by the band. "Walrus" is unique. "Fool on the Hill" is terrific melodically. Overall, "She's Leaving Home" is probably the best .
dannydingbat, Walrus is unique for a good reason, at the time Lennon had become sick of the pseudo intellectuals who tried to explain his lyrics and usually got it wrong, so he deliberately wrote the most ridiculous set of meaningless lyrics of all time.
He then commented to his lifelong friend Pete Shotton "Lets see what the silly ******* make of that"
If you google Pete Shotton you should find the story some where on the net.