My favorite countersink for wood has always been the square-drive ones used with a bit brace. They are easy to control and, when sharp, are quite fast.
I forgot to bring a countersink for a project I was working on today, and the only thing I had on hand were two that were made to cut metal. I have had them for a couple of years and use them to countersink the screws in the metal spiders on the candle stands I make, but I had not tried them on wood. Come to find out they work great in wood, too.
These are available from McMaster-Carr for less than $20 each. The two I have are part numbers 2724A122 (cuts up to 7/16″) and 2724A132 (cuts up to 9/16″). These cut the cleanest countersink I have ever seen in both soft and hard woods. They also work well powered by a simple hand drill.
— Will Myers