I wouldn't trust Platinum and Silver. The platinum supply scenario can change a lot if new deposits are found anywhere in the world, as the total market cap is very low. And silver is mostly used for industrial purposes, with less than 25% of the mined metal being used for investment and jewelry.
Silver's use in industry as well as jewelry and investments in the form of coins and bars is exactly the reason why I buy silver. It has use. It will always have a demand in industrial use due to it's conductivity and reflective properties.
Silver's use is rather limited
And these limits are twofold. First, there is in fact not much use for silver in today's economy on its own, and, what adds more injury to insult, it is not going to expand in the future (if anything, palladium seems to be a better choice now). Further, even whatever industrial use silver has, it is severely limited by its price which is to say the smallest rise in price will make this use shrink since silver can be easily substituted by other metals and materials. Indeed, silver is the best electrical conductor out there, but copper is not bad either, so it is just a matter of price
Why do you think that Palladium is a good choice when compared to silver and platinum? I know that it is used in catalytic converters, but how can you say that in future the demand for Palladium will increase?