Silver

Silver provides the best electrical conductivity of all metals. It is an order of magnitude less expensive than gold, but it has a tendency to tarnish (oxidize) and form sulfide which might have been exacerbated by the Industrial Revolution (thanks to burning coal). It is often used in low-loss waveguide components. The silver oxide layer is typically less than a skin depth so it has little effect on electrical loss.  Wire-bonding to silver oxide with gold wire might not go over well with your quality department. Silver pastes are often used in LTCC products in place of more expensive gold conductors.

All values except melting point are assumed to be at 25 degrees C, and may vary dramatically over temperature.