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

If you can get your DAC or preamp near the amp there is no benefit from a balanced connection, conversely if you want to drive mononlocks near the speakers balanced is likely the preferred option. In high res systems with short cables my experience is that balanced depending on implementation at worst is more sluggish or in the best of all worlds gives no discernible benenfit. Longer runs, balanced wins.