The binding post for earth ground or the binding post for the speaker output?
For the speaker output, use a heavy gold plated one and solder the internal wires with a high lead content solder. Avoid silver solder since the chances of getting gold embrittlement is much greater with the high tin content of silver solder.
Binding post for earth, just get a good one with lots of copper or brass in it. It is just a drain for leakage current so no audio signal flows through it. Or, at least, it shouldn't!