When selecting an engagement ring, it's also important to consider precious metals as well as the stone. You pretty much have two options: it's gold or platinum for the most part. Platinum is really the industry standard for setting diamonds. Not only does it enhance the reflective qualities of the diamond, but it's also the strongest and heaviest metal, and it's best to secure your stone for a lifetime. Yellow gold is great when used in the right context. For instance, it looks beautiful if you set it with yellow diamond pave, as in this stone.
Or to enhance the color of a yellow diamond. Sometimes the stone itself, the basket head, will just be set in yellow gold to enhance the color when the rest of the stones and the mounting is set in platinum. A lot of people think about white gold as a way to cut back on expense or that it will look just as good as platinum, but really, over time it starts to turn yellow because white gold is actually alloyed with nickel and silver to give it the white look, so eventually it's going to need to be polished and re-rhodium plated.
So, for the longevity of your ring, platinum is usually the best way to go.