What is the best metal for an engagement ring?

As a pure or nearly pure noble metal, platinum is much less likely to be chemically or allergically reactive to the body. So the chances of irritation are much less. As the main whitening agent in most white gold alloys is nickel, to which many people are at least slightly sensitive, this can be a rather important difference in itself. Platinum is denser and stronger than white golds. This means that settings can be made of thin, seemingly fragile constructions, and still have the needed strength and integrity to securely hold stones or jewelry together. Its density and strength combine as well to make it remarkably resistant to abrasion. Over time, Platinum simply doesn't wear away anywhere near as fast as white gold or other gold alloys, despite the fact that the actual surface hardness and stiffness of the white golds may seem much higher. Platinum's tensile strength and resistance to breaking exceeds that of gold, it isn't actually as stiff (for normal alloys). Unlike white golds, which even when annealed are slightly springy, platinum is a "dead" soft metal, which means it has little spring-back at all when bent. For setting stones, this is wonderful. You push a prong or a bezel over the stone, and it stays where you put it, without springing back just a little. This means that there is no need to bend a prong a little too far to get it to end up in the right place, or to otherwise have to fight with the metal to get a stone properly and safely set. Setting stones in platinum is less risky for the setter, and it makes it easier for the setter to use heavier prongs or bezels as well, when the design would benefit from it. You can set fragile stones more securely, and with less effort, in platinum They are safer when set, more secure, and the setter is less likely to have any problems getting it that way. And then, after all that, the setting will last, instead of wearing out in 7 to 10 years, as so many white gold ones seem to do. The color of platinum is its native color, and is not due to minority additions to the alloy. So you don't have the problem with surface depletion of the more reactive nickel that you get with white gold, which gives a white gold piece a dingy, slightly yellowish look needing to be repolished to restore the color after pickling. Also, platinum's basic color is a darker, grayer white. This happens to be very flattering to diamonds and other gems, making them look all the brighter; yet the basic white/gray color of platinum does not interfere with the gem's color. At the same time, the darker, grayer color of platinum also contrasts better with the yellow colors of gold, so two-tone designs can be quite dramatic.

Personally it depends on the women. I perfer white gold! I have heard its the best but like i said it depends on the womens choice

I think it's a matter of personal choice. Platinum is definitely more durable, and wears better, but it's also considerably more expensive than white gold.