Herr Joachim-
Silver, copper, gold is the correct order for those three.
Silver is the best conductor of heat and electricity, but expensive and scarce.
Copper is second. Cheap, widely available, almost as good as silver.
Gold is third, is expensive, but does not tarnish easily. That is really the reason gold is used.
Silver, gold, and copper are the Noble metals. They all are excellent conductors of heat and electricity. They are also very malleable and ductile.
Conductivity (relative to silver)
Silver 1.00
Copper .95
Gold .65
As far as the effect each has on sound, I will leave that to those who think they hear a difference.
Cable resistance has a minimal effect on sound, if the circuit impedance is correct, and you aren't talking about a power circuit. After all, the resistor, with the capacitor, are two of the most basic components in electronics. If resistance had a bad effect on audio, we'd be sunk.
Capacitance has the most affect on cable performance, coupled with the impedance characteristics of the circuit. And it is not changed on purpose to provide different grades of cable, but rather cable with lower capacitance can be more expensive to make. Other design factors also add to cost. Shield construction, jacket material, connector quality, etc.
I agree with your bottom line, though. Try a bunch of stuff until you are happy.