I had one of each for 24 hours in 2003, when I was buying.
For 0-60 MPH runs, and for 1/4 mile times and cornering, the Caddy is #1. For everything else, the Town Car is #1. (Which is why I bought the T.C.)
What's everything else? Comfort, interior luxury, overall seat-of-the-pants comfort, options, seats, carpets, door panels, overall "feel" ~ smooth ride, quietness, lack of wind noise, ability to have BOTH a cassette AND a C.D. autochanger, installed by the factory, and a hood that raises itself & a trunk lid that closes itself, among other features.