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

XLR.  My Digital Amplifier Co amps only have an XLR input.  They are supplied with a proprietary RCA to XLR adaptor.  My shortest run is 15 feet.

all else being equal - xlr

but the very nature of xlr is NOT equal to rca... at least if xlr is properly implemented

hope op understands that

a balanced circuit is not always behind a balanced connector on a backplate

this being said, single ended circuits and connections usually work just fine

From the top of my head: XLR has 4V rms signal level, RCA has 2V rms, so the signal-to-noise ratio (everything else being equal) is better for XLR. Second, the balanced connection means that interference on both signal lines would be cancelled out at the other end. That means that any kind of interference has less impact in an XLR setup. It also means that one bit more accuracy in all the analog signal accuracy that your expensive DAC has distilled from digital source ends up in your analog domain.

TL,DR: XLR is one bit more accurate. 

OTOH: there is no "everything else being equal" in audioland. Listen before buying, as always.

We are talking about 300.00 usd in cable no matter the cable manufacture. The fact we are even comparing cost is kind of moot for me. I suppose if I was buying someone’s off the shelf cable that would be the issue.

Because I don’t buy anyone’s brand I have the option for either balanced or single ended. I have the proof in the pudding here. Cables REALLY matter, the difference is I make my own, again it is REALLY NOT rocket science.. It is actually hooking up some wire ends to terminal ends.. OK you call it what you like.. THAT is what it is.. You may have to twist this and heat that, but guess what, it is still under 300.00 for 20 foot cable run of the highest quality cable on EARTH....

Depending on the gear some sounds different, but I have the option to change cable constructs a lot easier than most.

THREE kinds that’s all I found that work differently for RCAs and XLR.
Not talking about active shielding only shielding by design (weave) or wire twist...

I haven’t tried gold, aluminum or lead, BUT Copper, Copper clad and Silver are pretty predictable. The type of cover is predictable. How they are going to sound and how they are constructed make a lot of difference, but predictable. The type of copper NOT so much.

I keep seeing OCC is better, LOL I have tested the sonics on it until I almost went deaf.. OCC copper with teflon OFF the spool as direction is only .000X % less O2 free. I can’t hear the difference.. with RCAs or XLRs OCC vs OFC.

Speaker cable or copper/clad...that’s different... They sound different... OCC vs OFC

My answer is both, NO OR...