I tend to agree that DTS usually sounds "better", but I really think it's a subjective opinion. As others have said, the surround effects are more pronounced, but that's simply because DTS masters the surrounds at about 4Db higher than DD.

As far as DTS sounding "clearer", I think that comes from the tendency for DTS tracks to be a little brighter than the DD tracks, which sometimes makes things sound clearer, but not necessarily better.