Are metals or nonmetals better conductors of electric current? Why?
Metals, because of the low number (1 or 2) of valence electrons that they have.
Electrical conductivity in metals is a result of the movement of electrically charged particles. The atoms of metal elements are characterized by the presence of valence electrons - electrons in the outer shell of an atom that are free to move about. It is these 'free electrons' that allow metals to conduct an electric current.
The most effective conductors of electricity are metals that have a single valence electron that is free to move and causes a strong repelling reaction in other electrons. This is the case in the most conductive metals, such as silver, gold, and copper, who each have a single valence electron that moves with little resistance and causes a strong repelling reaction.
Semi-conductor metals and non-metals have a higher number of valence electrons (usually four or more) so they are inefficient or ineffective at electrical conductance. (https://www.thebalance.com/electrical-conductivity-in-metals-2340117)
A table of common compounds and their conductivities can be found here: