DTS has slightly better performance specs for their format than Dolby does. So it should sound better, right?
Well, the difference in the specs are very, very subtle for human hearing. But what isn't subtle (sometimes) is the mix. Since each version of a movie or recording is mixed different at each of the respected studios (Dolby / DTS) this is what is going to make the difference in sound.

I've heard the DolbyDigital soundtrack sound better than the DTS version on some movies and the DTS soundtrack sound better on others. So it really comes down to the individual movie or recording. I think when both are avaliable I usually like the DTS version the best, but it's close to half & half. When I don't like the DTS version it's usually because it sounds like they clip the peaks in some of the channels some times (pushing the dynamics to much) or put to much of an effect where it shouldn't be.
IMO