RCA or Optical?

Optical does not pick electrical noise or create one (no transmission line effects) but transitions are slow making it more susceptible to system noise, affecting threshold point and creating jitter.

Coax has faster transitions making it more immune to system noise but is sensitive to ambient electrical noise (needs good shielding) and transmission line effects - characteristic impedance of the cable has to be matched to one of the system to avoid reflections inside of the cable from impedance boundaries. Such reflections affect shape of transition hence level recognition point (threshold) resulting in jitter.

Because of all that digital cable is a system thing - what works for one system might not work for another or even exactly same system in different location.

+1 Kijanki. I have a very long run (8'+) from my digital cable box to my processor. The box had a bad SPDIF output, so went with an armored TOSLINK. Works perfectly. On the short run from my BD to processor, I found the TOSLINK far more listenablein my Mc gear. Having fun and happy listening are the goals, after all.

Optical are a pain to plug in behind a rack....