As I write this, one ounce of platinum is going for approximately $1,669. One ounce of gold is going for approximately $1,656. While platinum has historically been worth more than gold, that has not been the case in the last couple of years. It has just been in the last couple of weeks that platinum has been trying to overtake gold. I actually wrote a couple of posts on this back in 2011, saying that it might be a good time to look into platinum, although the price would have been slightly higher then than it is today.
I much prefer gold over platinum in an investment portfolio. I also prefer silver over platinum, although to a much lesser extent than gold. With that said, I am not against a little speculation in platinum. It is still basically on par with gold, so if the price adjusts to more historic norms, then platinum could pay off.
Of course, there is no magical ratio that has to hold. If you are familiar with precious metals, then you may hear about the ratio of the gold price to the silver price. While it can be a useful tool, there is no guarantee that some particular ratio has to come into effect in the future. There is no guarantee that the ratio has to return to its historic average. So the same goes for gold and platinum. But again, it can be a useful tool and tell us that perhaps platinum is undervalued as compared to gold, if the price ratio returns to more of an historical average.
While gold and silver tend to move in tandem (with silver having more volatility), there is less correlation with platinum and gold. Platinum has more industrial uses. Gold has a history of being used as money. Central banks do not accumulate platinum, at least to my knowledge. This has actually favored gold in the last few years because governments and central banks are buying gold more than they are selling.
If you want to speculate in platinum, here is my recommendation. With the price where it is right now, I would say it is reasonable to own one ounce of platinum for every $100,000 you have in net worth (excluding equity in real estate). That would put your platinum holdings between 1 and 2 percent. If you don't want to actually hold the metal, you can buy PPLT.
Although gold and platinum are not as highly correlated as gold and silver, I don't expect platinum to do poorly in the future, especially if we don't have a deep recession. One thing that platinum and gold do have in common is that they cannot be made on a printing press. As more Fed dollars flood the system, the nominal price of platinum and gold are both likely to go up.