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.

Balanced interconnects are mostly hype unless the electronics are fully balanced also
For example: on my Forte 4a amp are both RCA, and balanced inputs, but the unit is in itself not in a configuration to really benifit from using the balanced inputs. Also my preamp (an Adcom GFP750) has both balance and RCA outputs, but is not built as a fully balanced configuration.
Inmy case, and most, balanced output is created by using an opamp... not really the total electronic push-pull configuration that made balanced interconnects famous.
So in most cases, the balancd outputs are just fancy do-dads, for appearances only.
IF your pre, or amp, or D/A has a true balanced circuit topology, THEN yes use balance connectors... but otherwise not.
My Forte 4a amplifier when reviewed, showed using the standard RCA sounded better than using the balanced connections.
A caveat on that, if your suffering from electrical interference around the backs of your equipment, perhaps the balanced interconnects might offer a bit of relief... but that is a rare problem.
So, basically forget the balanced interconnect unless:
1) One of your components really is made with fully complmentary electronic circuitry.
2) You just want to impress SOME of your friends.
3) You have some interference problems that could be solved by using balanced (or shielded) interconnects.
4) You got the balanced interconnects at a steal /free price and why not use them.