Ah yes, what is money, really, and how is it created? Under the US Constition, there is only one kind of money; it's made out of metal, and the Congress has the power (and the responsibility) to coin it. In the postconstitutional Federal Reserve era, though, we have many kinds of money; principally 3: currency, open market operations, and fractional reserve banking.
The big question for traditional precious metals investors: will FRNs always be accepted as money, or will the marketplace someday demand a return to money in its traditional form? These folks have ben betting on the latter, but it's been a long, long wait. My personal investing horizon is somewhat shorter term than the period that has elapsed from 1913 to present.
I like silver because it is secondarily a monetary metal play, but it is primarily an industrial economy play. If FRNs are revealed as fraudulent, then those 90% coins that we all have squirreled away will be mighty useful. But if not, then silver is very attractive today, at its all time historically low real price, in twelve-year supply deficit, with increasingly tight above-ground stocks, and with a huge short interest overhang.
Whether or not you are looking for the end of the world, silver looks good right now.