Obtained a fine condition low serial number Gruen 50th that was perhaps one of many sold first time years later with a fine 14k white gold Gruen made case. White gold gruen 50th usually was 18k. It has fine original round dial not the sometimes pentagon form dial. I have 3 appropriate Gruen marked cases of right age: 18k white pentagon, 14k green pentagon, platinum and diamonds special form. Which, or none, best to use?