Which of the following is a good conductor of heat?

Diamond, silver and copper are good conductors of heat.

Silver is a nice conductor due to the fact its electrons are more free to transport as compared to the other elements, thereby making it more appropriate for the conduction of energy and heat than other elements. In metals, generally, free electrons are there which avert the switch of vibration of the metallic atoms to a few extents. But in diamonds, there aren't any free electrons. It is not a good conductor of electricity but is able to conduct heat due to its strong covalent bonding. Copper is able to retain heat well and for a longer period of time and hence is used to make cookwares.