Will you order that big juicy steak - rare, medium rare, medium or (gasp) well done? Well, the roast of your coffee beans offers you the very same choices. Sometimes, we prefer our steaks and our coffee beans one particular way every time. It is just a matter of taste! Nothing affects the taste of the coffee bean more than the roast.
Coffee roasters will start with green coffee beans. The more they are roasted the darker they will become. The lightest roast will reveal the origin of the coffee bean. The darker you roast a coffee bean the more it loses its origin flavor and takes on the roasting quality. I think you should find a balance between the two.
The very lightest coffee roast (cinnamon) is what most commercial coffee people offer in the cans you see in the grocery store. It is the most bang for the buck (cheap) and not my choice. The light roast does not allow the full flavor of the bean to be realized and will often taste sour. It has low body and the beans appear dry.
The medium light roast is a slightly darker brown color and still appears dry. It has just a little more body. Still not my cuppa joe......
A medium roast increases in darkness and acidity and the flavor becomes noticeable. The beans still appear dry and the acidity is much more intense with a more potent body.
Medium dark has a rich brown color and a small amount of oil is apparent. The acidity starts to decrease and the body becomes full. It is sometimes called City Roast. I think these are one of the best tasting roasts. You can still taste the flavor of the origin.
Dark roast is a brownish/black bean. It may be completely oily. The flavor decreases and the body dominates. There usually is less caffeine, less bitterness and less strength. It is generally slightly sweet. Because the darker bean has less moisture it will require a coarser grind and possibly more ground coffee per cup.
Very dark roasts are typically drenched in oil and the beans look almost black. The flavor is diminished. Interestingly, the aroma is lacking and the body is thin. This bean is often used in an American espresso. (There are some people who call this roast burnt) Some dark roasts are called Full City Roast, Italian Roast or Viennese Roast (and sometimes even French Roast). The origin of the beans will not matter because the roasting will mostly leave a strong smokey burnt flavor in its place.