Platinum is considered to be the "most precious" of the precious metals, and is your metal of choice, when only the best will do, and is also the choice of jewelry designers of fine heirloom quality jewelry.
Platinum is usually 90-95% pure. (We use a 950 Platinum alloy, where the other 5% is ruthenium.) White gold does appear slightly yellowish as it loses its polish and most commercial white gold is plated and will turn yellowish as the plating wears off. Platinum is always a cold light gray, and will retain its polish longer.
Platinum is more scarce than gold. The annual supply of platinum is only about 130 tons, which is only 6% (by weight) of the total Western World's annual mine production of gold.
Platinum does not wear down as gold does, so, over the course of a lifetime, your ring will remain virtually the same weight and size. Subsequently, platinum holds diamonds and gemstones more securely. It can be cherished for generations. Also, platinum is very unlikely to crack or be brittle during any sizing (or repair) operations.
Platinum evokes the future through the cool gray color and technological uses, but it also recalls the past. In the 1890's the Louis Cartier introduced the metal as a setting, and made it part of his most exquisite creations for kings and millionaires. During the first 40 years of the twentieth century, platinum was the preferred metal for wedding and engagement rings and was almost always used to enhance the beauty of diamonds and other gemstones. However, for the duration of World War II, platinum was declared a strategic material and its use in most non-military applications was prohibited.