Here's how I see it. Both DD and DTS are very good and very different encoding systems. Under clinical conditions both should be indistinguishable from each other, and please remember that you can't compare the DVD versions(for starters you have to turn up the DD version by 4db-8db or more depending on the release)
My opinion is that DD and DTS have different objectives, DD tries to be a transparent transport for the master track, whereas DTS tries to up the ante and give a 'better' presentation of the master(similar to the "Disney Enhanced Home Theater Mix" on some of the Disney SE DVD's like 'Aladdin'), whether thats a good thing or not and whether they achieve their objectives or not is up to the individual.
cheers