When choosing your plating, keep in mind that each time a tactile dome is pressed that the legs or outer perimeter of the dome flexes. This can rub on the circuit and cause deterioration of the circuit pad over time. Both nickel and gold plating are options, but the type of plating depends on the amount of actuations you anticipate for the life of the application. For higher life applications, harder nickel or gold is needed. Lower life applications can get away with ENIG plating. Read more here.