Bad coffee is made palatable by over-roasted it, which helps burn off poor quality notes and oils. Of course, this also burns off what little good notes and oils it might have had, but the result can be a net-pleasing effect if desperate for a coffee flavor. Look up the history on “French Roast” to see how this was arrived at in history.
“French roast” and “dark roast” take advantage of poor quality beans. “Light roast” and “medium roast” are the roasts capable of leaving all or most of the flavor notes in the coffee, but this can also mean bad notes from any lower quality beans are noticeable.
You should want good tasting, “light” or “medium” roasted coffee. Definitely don't pay extra for the other roasts, which would kill the life out of good coffees (as over-roasting gets rid of their flavor characteristics, wastefully so).
How do I know this? Aside from having read about this, I now have family who maintain large coffee plantations.
Can we get your opinion on “blonde” roasting?
Oh and, if it happens, please ignore any response to this post by Lazamataz.