I say: use silver. Either DIY with 1mm 99,99% silver and cotton or teflon tubing. If not DIY than I think ViaBlue (copper & silver) has best price/quality ratio. I think it is better than Kimber 8TC (copper). Extreme deep bass but very tight, extreme open highs - that means you need high quality equipment for using ViaBlue. The copper Kimber 8TC sounds smoother and not as tight but also very very good.
Till now ViaBlue has beaten every other speaker cable I tested: Kimber, Nordost, Naim, Linn, Triangle, Monster, MIT, Restek, Sommer and others.
ViaBlue is extremely good but dangerous, it is unforgiving.