Aside from all the other possibly subjective influences, speech is definitely clearer to my ears via DTS. I used to try both soundtracks and then note which sounded better, again to my ears, but found after a while that I either prefered DTS or found no difference. I never prefered the DD soundtrack so now I always select DTS if it's available.
Ayreonaut mentions the dialogue normalisation being a DD feature, but even when I select DTS my 3806 briefly displays the dialogue offset (usually -2 to -4dB) as the full multichannel mix cuts in from the DD 2.0 used during the menus.
The two bottom PDFs
here make interesting, if technical reading from when Dolby puplished it's "findings" on DTS. It would appear to refute JCDs understanding as regards to the original directors/sound engineers/etc input or not in the DTS mastering process. I am not saying this is any more or less true than anything Dolby might say though.
Russell