Uncompressed or Dolby Digital Blu Ray Audio

[HDefinicktion]

I was hoping that someone could either enlighten me, or send me to the right info...I have been trying to figure out the audio tracks on Blu Ray discs.  I don't know which one too choose...the 5.1 uncompressed track or 5.1 Dolby Digital track.  Once selected, what setting does the receiver need to be on...Auto, PCM, Direct...I am not sure.  I have been able to hear them both, so I know that the receiver is picking both the tracks up, but they both sounds different...DD seemed much more quiet and not as discrete as the uncompressed.  The Denon receiver displays the track as DD PLII which is Pro Logic II...I was watching Pirate of the Caribbean.  So...which track do I select, and why?

Thanks