Costa Rican coffee IMHO is the best out there with Sumatran coming in a distant 2nd. I prefer a dark roast and I enjoy my coffee black.
After going to Costa Rica and tasting the coffee at each step of the process, I can tell you that the dark roast is used to hide an inferior product. Like burning toast, it adds char and taste, but completely overcomes the regular taste.
For coffee that is poor, burnt is the only way you can make it taste the same every time.