Silver is the best metal conductor, but graphene is the best overall material at conducting electricity. Graphene consists of carbon atoms arranged in extremely thin sheets, and has the lowest electrical resistance of any commonly known material.
Most of the best conductors of electricity are metals. The best conductors are silver, gold and copper, while the worst are mercury and certain alloys of stainless steel. As a general rule, elements with a single valence electron are better conductors than those with more. They are able to displace electrons easier to allow the passage of electrons from electricity through the material.