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.
TL,DR: XLR is one bit more accurate.
OTOH: there is no "everything else being equal" in audioland. Listen before buying, as always.