Platinum is the most durable of the three and has a slightly duller finish than the others, but is also the most expensive. Gold is somewhere in the middle where prices are concerned, but has the most variety. The three basic colors are yellow gold, rose gold and green gold. The green and rose gold are usually associated with Black Hills Gold designs, but you can find it in other designs if you look hard enough. Yellow gold is the most common and the most widely available.
Gold also comes in different combinations where it is mixed with another metal.
The most durable of these is 10 kt. gold, and the least durable gold is 24 kt., which is pure gold. Yet another is to buy a ring with a stone in it other than a diamond. One way to do this and still have the symbolism of something special for your engagement ring is to use your birthstone. If your birthstone doesn't appeal to you or if the price is still prohibitive, such as is usually the case with good diamonds and good emeralds, a nice idea might be to get your partner's birthstone in your ring. You could even say that it's symbolic of two lives coming together as one.