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

Locking grip?, sluggish? 

Over short distances they sound exactly the same. Over longer distances balanced cables have a theoretical advantage but I doubt any of us could reliably tell the difference. XLRs are certainly more ..hip. They lock in place which is nice. For those of us that use mono amps behind the speakers they could be considered mandatory and this is where they first entered the consumer Hi Fi chain then got generalized. They make sense for turntables which are balanced from the get go. Sound different? In your dreams maybe.

Many comparisons with various gear over 2 decades shows that dynamics are better, contrast is better, low level detail is superior and bass definition and impact are improved with true balanced XLR cables used with true balanced gear ⚙️ 

I have recently started using the XLR version of Van den Hul The Second instead of the RCA version (both one metre lengths) between pre-amp and power amp, and have been pleased with the outcome. Not an earth shattering improvement, but to my ears there has been a subtle change for the better.

I agree with dave_b. I have even noticed a big difference using an XLR  jumper from RCA too XLR.

i agree that for some, long runs across areas with strong sources of interference will show the benefits of xlr connections and cable, but i suspect that in just as many (if not more) cases the apparent sonic ’benefit’ is due to the balanced source delivering twice the voltage swing to the receiving component

lots of people fail to properly compensate for volume differences and are swayed by the subtly (or not so subtle) louder version they hear

in any a-b comparison loudness compensation is absolutely critical -- our ears are impressed by 'louder', even by fractions of a decibel