All things being equal (hypothetical) which do you prefer, XLR or RCA?

Dual differential XLR is less prone to interference but can be a bit sluggish compared to the best single ended implementations. Single ended is preferred on purist systems based on SET amps from Kondo, Shindo, Audionote or Wavac. I guess the easiest way to look at it: short runs in low interference environments RCA, otherwise XLR

Not so hypothetical as some companies offer both rca and xlr connections on single ended only equipment for purely convenience sake. In these situations, I prefer xlr for their more secure connection and strain relief.

Over the past year, I've had a couple of opportunities to compare RCA vs XLR interconnects of the same brand/model, length (1 meter). The XLR's definately sound better in my system. More open, solid image, detail. Connected between a Marantz SA-10 and PM-10. Maybe those particular components were designed to be best with XLRs.

Thanks for the responses! @testpilot and @ron_hartman these are EXACTLY the kind of responses I was hoping for - thanks Folks!

The AES48 stadnard is what you should look up. Atmasphere has stated a few times on this forum that many manufacturers do not implement this spec properly. That is a main reason why various cables sound different and also why XLR and RCA also do not have much difference on those units.

My gear does support the AES48 standard and using anything but XLR is a waste of my money. Actually on my Benchmark gear I have to use XLR on the amp.

I run long XLR cables between my preamp and DAC and have the benefit of moving the rack far away from the speakers. I would not try that with RCA cables.