Paul McCartney. I think just being dead gives some bias towards Lennon.
Overachievement lecture:
McCartney's music generally tends to be more upbeat than Lennon. A perfect example is
Maxwell's Silver Hammer, one of my favorites. It's about Maxwell going around and murdering people while still managing to be one of the most upbeat of all of them.
I think Lennon can be 'deeper' in some of his lyrical capabilities, but some of that perspective is also based on philosophical over-thinking on our part. "Words are flowing out like endless rain into a paper cup" was written down while his wife was lecturing him about something and he wasn't listening ("words are flowing out" = "You won't stop talking"?). Along those lines, many of his pieces seem to be more drug influenced than 'deep'. I don't really have anything against drug use, I've done enough that I'm not in a position to judge

. I just think that it is, again, overly credited as lyrical philosophy.
In 1965-67 is when they were doing LSD. McCartney apparently used it a few times, Lennon seemed to be more of a regular. He even took it while they were recording Sgt. Peppers, although this apparently was accidental. The others ended up stopping the recording session. Lennon then moved on to heroine, several songs on
The Beatles album seem to refer to it.
For me, I look at some of the songs he wrote during his different drug periods. Many are generally accepted as him talking about the drugs, but great nonetheless. This is all much more theoretical and assumptive than true knowledge though.
Sorry for another essay, I just really can't help myself. Once I start I don't shut up...