I've always used a dark rum. Bundy packs a punch right up, but there was this other locally made brand that I brought a while back and used it to make rum balls for DD2's teacher - well I didn't think it really hit the spot even after 4 tablespoons, but OMG, all it needed was to rest and they packed a hell of a punch later on! Bundy is your best bet because rum balls just aren't the same without real rum in them.