What's better: RCA or XLR?

Balanced is better because you lower the noise floor and get 6db's of gain and usually cancels out any hum that your system may have. Most high quality cable already has the negative conductor inside and you can just add the XLR's yourself.

There is a reason that pro sound and recording studios run balanced. But, I guess the main thing is less noise and signal loss with long interconnect runs. Another reason in pro sound is the ability to hook cables together when longer runs are needed.

Robt.

While it is usually best to have a fully balanced system I did get rid of a hum problem that I had with my amp by putting XLR's on the amp end of my interconnects and leaving RCA's on the preamp end. I eventually added XLR outputs to my preamp. Even though it is not a balanced design, I like the better connection that the XLR's make.

Well stated. The best balanced component uses mirror imaged circuitry. But, designers have switched to balancing transformers such as Roland Research.