I guess it depends on how you will use it. If it is just to be used for show and some light shooting and hunting the skeleton butt is ok. They certainly look nice and show off the gun makers art a little more. But I feel that if you will use the gun seriously a pad or a plate should be used. I like thin rubber but pads. They don't slip and you don't have to worry about putting them butt down in the rack at the club. When I see a skeleton butt all beat up and the metal blueing scratched from putting it in a verticle rack or sitting on the concrete it makes me sick. I use to put my Parker repo muzzle down in the rack at the club so I would not damage the plate. The base of the rack was wood so no damage to the muzzles either but what do you do if it is the ground or concrete? You may be stuck trying to find a safe place to lay your gun while you have your lunch.
I'm with Tanky on this one. While there's no question that a skeleton or heel/toe set is classy looking, they're not so practical for real use, IMO. Furthermore, a "self butt" looks to me like a cheap air rifle that wasn't finished. The bare wood is even more vulnerable to scratches and damage. My guns will end up with at least a thin pad on them. Stays in the rack better, soaks up at least a tiny bit of recoil and mainly because they ARE my guns.