I would pick Sondheim cause he's the master of intricate, meaningful rhyme, double meaning, and allusion . His lyrics and references are fun to decipher, just like you'd decipher a poem. He's not as vaguely "poetic" as some other writers, but he packs a lot of meaning into a little bit of space, one of the hallmarks of good poetry.
-Was that a fart?
-My fault, I fear.