<<Hrmm.. so what yields the best clean hole? >>
like i said, use a power drill. but when you drill the hole, be sure to push the drill in and out a couple of times to make it clean. actually use a bit that is a little smaller than your existing belt holes. this is because once you push and pull the drill in and out of the hole to make it clean, it'll end up making the hole a bit bigger than the bit.