The answer begins with a question, are you looking for long term investments or short?
Silver and Platinum fluctuate but with with the same degree as gold. Over the last two months gold buyers (who are required to hold second hand jewelery they buy for thirty days) lost thousands of dollars over the last two months because gold dropped more than $300 from the price they purchased. If you go for gold know you are in it for the long haul, but I see it steadily dropping. I am hoping it settles under $1000. because that is best for the ecomemy.
Silver was driven up a few years ago, but dropped down to around $20 an ounce which is reasonable, though $15 would be better.
Platinum took a huge drop a few years ago when auto makers quit make catalytic converters, at the same time gold started increasing in value. What happened as a result was jewelers turned to using platinum as alternative white gold. It a better metal anyway. Platinum has since stabled and I for one think of it as a more sustainable metal.
If I were investing it woudl be platinum.