Agree with "not the medicine cabinet"
but I think since you are not planning "on your person", go for as big ( within reason ) a hand gun, as you can fit the it's respective hiding place... emphasis being on easiest to shoot accurately, rather than your typical bug or CCW gun... a 4" barreled revolver, or full size auto, will typically give you a better controlled shot, & can yield higher capacity, & can / could add more to the intimidation factor ( just choose either calibers ( or the frangible bullets ) needed to as safely as possible, shoot a bad guy without dangerous over penitration ( guess that 500 S&W wins in intimidation factor, but loses in the accidently shooting your neighbor, through several walls, catagory )
also agree with choosing a fire arm finish that fits it's storage environment, like stainless for the bathroom...