This is interesting information is taken from "http://materials.globalspec.com/help...12§ionid=1
"Copper is second only to silver in bulk electrical conductivity. Copper has superior strength compared to silver, but inferior oxidation resistance. Copper is often employed as a base metal in electrical contact and electrode applications.
Silver has the highest conductivity of all metals. The high conductivity, softness or low hardness and high resistance to oxidation make silver an excellent choice for contact materials. Silver is strengthened with additions copper, but at the sacrifice of conductivity. Fine silver is silver with very high purity (99.99% Ag). Pure or fine silver is too soft for most commercial applications, but the material is used as a starting component to form other silver based alloys.
Gold has extremely high corrosion resulting in high reliability electrical contacts even under light load conditions. Gold forms useful contact alloys with silver, copper, nickel, cobalt, platinum and palladium. Major drawbacks are high cost, poor sliding friction characteristics and low erosion resistance."