I will stand by Hot Rats 'til the bitter fucking end. "Willie The Pimp" featuring Captain Beefheart is an awesome song.
It is a good song, but I have to give most of the credit to Beefheart for the awesome vocal - that's what really sells the song for me, especially since Zappa has a long history of either choosing horrible vocalists or, even worse, performing the vocals poorly himself. Jim DeRogatis played "Catholic Girls" on this week's Sound Opinions podcast and hooo-boy it brought back into focus just how God-awful the majority of Zappa's output is (for me, anyway - I'm not trying to run down yours or anyone else's tastes, JJ).
Having said that, I really do need to hear those early Mothers albums again.