I haven't seen either movie. How do each of these killers murder their victims?
In this respect, they're both really well matched. They both have used their bare hands to strangle and/or break necks. They've both used strands of Christmas lights to garotte their victims. And they've both grabbed pretty much whatever is available and killed with it. In the beginning of
Black Christmas, Billy escapes from the institution for the criminally insane by stabbing the guard in the jugular with a candycane he had sucked to a sharp point.
In
Silent Night, Deadly Night, the other Billy picks up a girl and impales her on the horns of a mounted reindeer head.
However, throughout most of
Silent Night, Deadly Night Billy was using an ax to kill his victims. Plus, under that Santa Suit he's very big and muscular. Much more intimidating than some sickly, jondaced "Joe Average" like that other Billy.
However, in the 2006 remake of
Black Christmas, Billy killed as a part of a team with his inbred sister/daughter, Agnis. If you were to work that into your calculations, BXM Billy might have an advantage over SNDN Billy.