BNC or Coax?

BNC is a cable connector - coax is the cable that goes between the BNC connectors. You are comparing apples to oranges.

I suspect that you meant to ask whether a BNC connector or an RCA connector is preferred. The answer would be the BNC connector -- it is designed to handle high frequencies, and will provide a better impedance match to the cable (which is important for relatively high speed digital signals such as SPDIF, although unimportant for analog audio signals).

Regards,
-- Al

Thank you all for your replies.

I do understand that BNC is a connector, not a cable.

My understansing is that HD video signals (like from DVD and BD) are faster (greater bandwith?) than digital audio signals (from CD, PC). I have heard that BNC beats coax for video (via composite analog or by 75ohm digital), but is about the same for digital audio. Comments?

I have heard that BNC beats coax for video

Once again, BNC is a connector, and coax is a cable, so your question is unanswerable. Assuming you mean to ask whether a BNC connector is better to use for both video and digital audio than an RCA connector, the answer is yes (although either connector could very well be acceptable in both cases).

Regards,
-- Al

As Almarg says, coax is a cable. The name is a short form of "co-axial", which means that the central conductor and the woven shield share the same axis in cross-section.

Also as he says, you can fit an RCA connector or a BNC connector to a coaxial cable.

You could also fit twin-lead cable to an RCA connector but IME it would be a bit harder to do that with a BNC.

Other connector types can also be used with coax cable. Phone plugs for example.