Silver wire is used for some things, but it is a lot more expensive than copper which rules it out for most applications.

Here is a table of the conductivity (in units of 10^7 S/m), the density, and the cost of copper (Cu), aluminum (Al), silver (Ag), and gold (Au).

               Cu    Al      Ag       Au
  Conductivity 5.96  3.5     6.3      4.1
  g/cm^3       8.96  2.6    10.5     19.3
  $/kg         9.03  1.2  1030    92100

If we had a copper wire with a specified capacity in amps, here is what aluminum, silver, and gold wires of the same length and capacity would weigh and cost as a percentage of the weight and cost of the copper wire, and what their diameter would be as a percentage of the diameter of the copper wire.

      Weight  Cost  Diameter
  Al    49       7    139
  Ag   110   12646     97
  Au   310 3190000    121