Dolby Digital is found on most major streaming services as well as DVDs and Blu-rays, while DTS is less common. However, DTS operates at a higher bit-rate and edges out DD in terms of quality.

Dolby Digital (Downmix PCM or Dolby Digital) BD Audio Settings (Mix or Direct) DTS (Downmix PCM or Dolby Digital) 48Khz/96Khz PCM (48/16 Bit or 96/24Bit) ...

I believe that PCM is when a 2 channel digital audio (i.e. CD type audio stream) is fed through the digital connection to the receiver. Bitstream is multi-channel audio (be it DTS or DD).