To balance or not to balance, that is the question

TRULY balanced operation will yield exactly a +6dB increase, possibly lowered noisefloor, resulting in more perceived detail and top octave air.
Fully complementary balanced designs thus usually sound better when run correctly (XLR) rather than just single-ended (RCA). FAKE balanced operation will have the same loudness as single-ended, and thus no advantages. Hope this helps.

If your pre and amp are balaced CKT, use XLR cable.
You will find gain is ~3 dB higher, i.e. louder at the same preamp vol. position.
The bass is tighter and high has better resolution, and the sound is overall "cleaner".
It does sound better, not just impress any friend, if it is really balanced CKT.
If your amp's are not balanced CKT, they probably sound about the same in RCA or XLR. In this case, RCA is usually cheaper cable.