Coins and Paper Money
Collecting coins has the built in safety factor that they will be worth at least their face value. After that, value is basically determined by the market price of the metals used in their striking, and the quality of those metals. Gold and silver coins are the only ones worth collecting, and even then the greater amount of these precious metals in the coins is crucial. Flaws, limited minting, and other characteristics are enhancing factors, not final determinants. There are plenty of reliable guides available for those interested in coin collecting to protect against bad investments. Paper money, on the other hand, has limited collecting value. The principal reason, is that governments can remove paper money from circulation at any time, rendering it worthless. Unlike precious metals, paper does not increase in value.