Copper is a better conductor than Gold, however copper oxidizes readily when it is exposed to air. This causes its electrical properties to decrease. The reason you see gold-plated connectors on a lot of electrical cables is because gold does not oxidize (anywhere near as quickly as copper). This allows it to maintain its conductivity, and therefore its reliability as a method of transporting information.

The Handbook of Chemistry and Physics or the primary literature would do just as well.

Also, OP didn't specify temperature.

If we're talking about the maximum conductivity possible superconductors would by default be the winner with the zero resistance and all.

This. Because the conductivity is temperature-dependent, the order may change at temperature values away from 20 C.