Man, that's a tough question. I definitely like the latter Beatles stuff better, but the early-later stuff was good too, if that makes sense. I'm talking Rubber Soul/revolver era. At a push my favourites (both lyrically and melodically) are:

In My Life
Come Together
Get Back
Revolution (all versions)
Happiness Is A Warm Gun
Helter Skelter
Here, There, Everywhere
Tomorrow Never Knows (Great Drumbeat)
Let It Be
The Ballad of John and Yoko

I also have a soft spot for Free As A bird. It almost makes me cry hearing John Lennon's crackly home recorded voice from beyond the grave.

And the worst?

Ob-La-Di, Ob-La-Da or anything by Ringo - Don't pass me by - what was that? Almost killed the White Album with that one.

I'm a Lennon man myself, although there are a good few McCartney tracks in my list. I saw McCartney live recently and there is just something distinctly uncool about him. I've heard good things about his new album though.