I use a youth model, 20-gauge, pump. A youth model is shorter and better for CQB (therefore more maneuverable inside the house). It affords less recoil, therefore more controllable for the smaller framed family member. It has less possibility of over-penetration of sheetrock walls. Mine is an 870 Remington, but a Mossberg 500/590 is just as good (I carried a 590 during some of my Army adventures). 18 inches is the minimum barrel length for a shotgun per the NFA of 1934. An 18 to 20 inch barrel is best for security scenarios. Inside a room, whether it is a 12 or 20 gauge is of little consequence!