Drill bits
I have found that sometimes an oversize drill bit work just as fast and better than anything with a 100 degree cutter.
Depending on how the hole was drilled, especially if the drill bit is less than real sharp, the burrs may be pressed out to the side. By the time you use a countersink as a deburring tool to remove them, the hole has been excessively deburred. Drill bits have a 118 degree included angle which makes them a little "flatter".
I hold the drill bit as square as possible to the hole and twirl it between finger and thumb using as little pressure as possible so the bit won't cut in. Seems to do a real good job.
The only other recommendation I have is the E-Z burr tool (I think that is the correct name) which deburrs both sides in one pass. It can quickly over-deburr as well but works in tight spots.
Dave A.
6A build