The answer depends on what emergency you are preparing for.
►Profit - a place to store your money until you need it for when your car or refrigerator breaks down:
I don't invest in precious metals for profit because on the average, their value only keeps pace with the inflation rate. As an investment, that is better than burying your money in the back yard, but not by much.
There are better ways to make a profit.
►For a loss of value of currency:
In an economic disaster where the currency is quickly losing value, everyone will be rushing to buy any commodity they can while the money can still buy things. The shelves in the stores will be empty. (This happened in Russia recently where their currency dropped in value by more than 30% overnight.) Silver will hold its value and you will be glad you have as much as you could get.
►For an economic collapse where trading is still going on:
I recommend pre-1965 silver U.S. coins that have no collector’s value. They are easily identifiable by the general public, their value is well known and they are in small, easily tradable units. Nearly every household has a few of them in the back of a drawer collecting dust. After a currency breakdown, these may become the “coin of the realm.”
Silver rounds, silver bars or gold coins would be difficult to trade. Most people could not distinguish a platinum coin from a bus token.
How much to have on hand? In a partial economic collapse where trading is done with silver, $500 in silver coins (face value) will be far more than 99.9% of the households will have and it will be more than you need.
►If the collapse is worse, then silver will be of no value. You would not be able to buy the last can of food in town with all the silver in the world.
A person should begin survival preparations by stocking the pantry.