I can't do my "single greatest line" because it would take a long time and I'd come up with a long list (some of which have been mentioned already). But there's something about some songs in their entirety that can't be captured by just a few excerpted lines. The whole song, music and all the brilliant lyrics together (which just aren't quite as good apart), just builds to evoke something. Big ones in this category for me are Gone, Stay, Bad, Kite, Walk On, A Sort of Homecoming (easier to excerpt but not the same as all together), One Tree Hill (again easier but the whole is better than the sum of its parts). Mercy too. Songs in this category tend to be on my list of favorite U2 songs as well.
And I agree that
I'm just hanging on/to watch you go down
My Love
is incredible and spine chilling. Also,
Between the horses of love and lust/we are trampled underfoot
is also brilliant, along with
she wears my love like a see through dress/her lips say one thing, her movements something else
So Cruel is full of brilliant lyrics but for some reason it doesn't add up to more for me like the songs I listed above (it's still one of my favorites though).