XLR or RCA cables?

XLR is quieter  especially on long runs with better resolution.

I use a couple of different CD players (one with XLRs, (fully balanced), and a few with RCA outputs only.
I get much louder volume out of the balanced XLR connection player than the RCA connection players when they’re hooked up to my preamp. (I could compensate for this on the preamp, but just turn the volume up for the RCA-only players.)

I tried a pair of silver-alloy XLR cables, and the sound was too bright for my tastes.
I switched to an all-copper pair of XLR cables, and it is much more to my liking.

As with all things, you have to pick what sounds good to your ears, and sometimes the cheaper cables sound better than the more expensive ones (case in point above). They do make a difference, though.

I will say this.....I will go out of my way in the future to only buy components with fully-balanced XLR outs on them, (as applicable).

@vanson1

In my very limited experience, I have found XLR to be quieter cables than RCA cables, tending also produce a truer sound, without significant coloration.  With a truly balanced system, supposedly you're not supposed to hear a difference between XLR cables, there are probably few systems that are truly balanced.  While my entire system is not truly balanced, I found that the Mogami Gold shielded cables were as neutral as any.  Some XLR cables that I listened to (which were quite expensive) were just bad souding.