It is really a matter of personal preference... The four prong setting will leave a little more of the stone's surface exposed, but it tends to create the optical illusion that the diamond is square (the prongs pull the eyes out to the corners) and there is more risk of losing the diamond - the diamond can fall out of the setting if a single prong is pulled back or snapped off... A six prong setting is more secure - three consequitive prongs must be pulled back for the diamond to be removed... And the diamond will continue to appear round... Either way, be sure to have the diamond ring inspected by a qualified jeweler every three months or so for metal stress and to ensure that the diamond is still tight in the setting... Don't twist the diamond to determine if it is loose, you will loosen it in doing so