I think his best lyric is "Stop Me If You Think You've Heard This One Before". In a way it's an odd song to choose, because it has some quirky, throwaway lines and it's not nearly as epic as "The Queen Is Dead" or tracks like that. It's my favorite because when Morrissey is praised for writing about things in pop music that no one else has written about, they mean songs like this one. To capture a love affair at the moment it dies, but before the self-deceiving and disinterested party backs out, is such a fine observation to make in a pop song, yet he does it with such broad humor. Other Morrissey lyrics are about why he can't find love but without "Stop Me" those songs wouldn't have as much meaning. "Stop me" shows that Morrissey knows what relationships are really like, so when he sings of "emotional air raids" and the hopelessness of empty beds it doesn't sound like cheap melodrama.
(The only other point to make about "Stop Me" is that Johnny, Andy and Mike turn a brutal uppercut into a knockout roundhouse. Morrissey's lyrics don't exist in vacuum...)