For lyrics only, how 'bout "In My Life"? That's the first to come to my mind, a John Lennon masterpiece covered by many other artists. (I think Judy Collins was the first.)

McCartney's "Yesterday" is the single most-covered song of all time, and his "Michelle" is right up there, but I'm not sure whether either of these sentimental ballads would be all that impressive when the lyrics are read without the music. People sure like the songs, though, and request 'em all the time.

I don't agree that the Beatles' early years were "better" musically than later. I think they continued to develop & get better in every respect. They did become increasingly *separate* songwriting personalities with time -- the Lennon-McCartney partnership was "in-name-only" after the first few years (as soon as they achieved international fame, actually), and George Harrison emerged very gradually as a significant songwriter on his own.

I am continually more and more impressed by George's work; every one of his songs is completely diferent from any other, of his or anyone's.

In fact, George's "While My Guitar Gently Weeps" might hold up to scrutiny from a lyrics-only point of view, I don't know; it's hard for me to separate the lyrics from the music, especially since the song is *about* its own instrumental sound.