Question about cables.

RCA or Optical?
That is apples and oranges. RCA is an analog connection and optical is a digital connection. What components are you wanting to connect?
If you are referring to digital coax that uses RCA connections then check out Blue Jeans Cable for some additional info. They prefer digital coax as it is more robust over a long distance.
Just like your misplaced question about 5.1 vs. 7.1 in the analog forum a few days ago, this question too is better suited in the Home Theater or Digital forums. You'll get more responses in those forums.

Also it may help to provide a little more info when asking a question too such as Digital Coax (that has an RCA connector) vs. Optical.