Hey Jude, Let it Be, I am the Walrus, Here Comes the Sun, Revolution, and With a Little Help from my Friends
I used to have so much difficulty with this, but now I'd say it's A Day in the Life, hands down.
Also, add me to the people who actually like Revolution 9. It didn't happen for me though until I enrolled in a university music composition program that had a lot of computer music majors and... let's just say that compared to a lot of the stuff those people do, Revolution 9 is pretty accessible. After you've had to sit through some pompous grad student giving you what's basically 17 minutes of guitar feedback, Revolution 9 is nothing.
Plus you can have a lot of fun listening for the different clips he samples in there (Sibelius for the win!)