I cam across this webpage the other day explaining the differences between owning silver coins and silver bars. One of the things that struck me was the difference in liquidity between coins and bars. Naturally, coins have a greater liquidity simply because they are smaller in both size and value. However bars can be obtained at lower prices per ounce.
My conclusion is that if one is buying silver simply as an investment (to make money) and not as a long term hedge against inflation, then it is better to go with silver coins since they are easier to sell. If there is one thing to be said about silver, it has a history of volatility, and if you ever need to unload them in a hurry, you want to have the most liquid form available.