XLR or RCA?

I'm mystified that RCA and phone plugs are still around, but I have to accept it and use them daily...there may be an argument for RCAs taking up less space, but after many years of using XLR mic and balanced ins and outs of live sound mixers and recording stuff I'm an athletic supporter of XLRs, even when not part of a balanced system. When I'm declared Ruler of the Universe I'll demand Neutrik Speakon connectors and XLR plugs be universally used all the time. Besides, Neutrik Speakons are made in Liechtenstein, which should be all you need to know.

XLR balanced low impedence cable signals can run 100s of feet with ZERO noise.

I used a new pair of balanced cables into a decidedly non balanced but XLR friendly power amp, and they sounded like crap. Seriously...replaced them with much better XLR cables and all is well (although in this case I could be using single ended cables I do prefer the XLRs anyway). I noticed some substantial differences between brands of ACTUALLY balanced cables when mixing sound with headphones from a live feed (TV show production). Even with truly balanced signals I can say that better cables can sound much better. Who knew?

Fully balanced signal is what makes live sound reinforcement buzzless and clean (except for electric guitar players with noisy single coil pickups)...with 100 foot (or more) snakes. You can take an unbalanced signal cable from a live musician's instrument pickup, stick that cable into an active "direct box" that changes it into the balanced signal the mix needs, and the result is clear as a bell. Also, the "future" is wireless live mixing (use an iPad).
When I play electric guitars I end up using long runs of unbalanced guitar cables (all the stomp boxes with an input cable and out to the amp) and have to apply small "micro amp" boost in there to unload the pickups and retain a modicum of fidelity. Nothing quite like a modicum of fidelity.