Any films RELEASED with DTS should have a DTS track or version and DTS remixes only if the soundtrack can be remixed from scratch in DTS.
The two Fantasia DVD's sound great in DTS (Orchestral sound is great in DTS) and so do films with very detailed sound.
The DD 5.1 track for North By Northwest is perfect and DTS wouldn't really enhance it since it was only remixed from separate music, dialogue, and sound effects tracks (not the stems)
On the other hand, the DTS remix for Terminator 2 works great since it was remixed from the ground up.
In my opinion, silent film DVD's should eaither have the music track in DTS or PCM. You need rich and full sound when it's just music. (The PCM track on the City Lights DVD is fantastic...)
DTS would be nice for mono soundtracks since it wouldn't take much space with just one channel (DTS mono exists since Woody Allen has used it.)
How do you know which one sounds better without actually watching a large portion of the film?
Anyway, to answer the question, I always listen to the DTS track if its offered. For the most part I never listen the DD track if the DTS is there so I couldn't even tell you if the DTS is better than the DD its just force of habit.
DTS whenever available, if a DTS version is available on a different disc (as Jurassic Park) I'll get that version, for me it just sounds better, but that just me..