A few points to make your decision:
Junk silver (90% silver coins from circulation) tends to have the lowest premiums (which means you'll pay less up front, but also get less on the sale).
It tends to be widely recognized and accepted (if you have some off brand or highly counterfeited bullion rounds or bars, it may mean a more difficult sale).
Junk silver is often sold at a certain amount x face value, but because of production variation and wear, may contain less silver than when new, so some places buy it back by weight rather than face value.
Junk silver is more difficult to stack and store- more pure silver in bars takes up less space.
Junk silver is good in a potential bartering situation- you can spend it in dimes, quarters, halves, or dollars vs. by the ounce with bullion.
Junk silver has cool historical value- you are holding old coins with cool designs. However, bullion can also have cool designs and some people collect them like art.