I'm not comfortable yet with shotguns. Every time I've pulled the trigger I've flinched. For me as a novice shooter, comfort and confidence are by far the most important aspects. If shit hits the fan, I can't be afraid of my weapon and the intruder.

Also I already have a modest rifle (my training wheels gun: 9mm PC Carbine) and part of my thinking for the pistol is to have it secured in a small, secure space in a different part of the house in case the rifle is out of reach. Much easier to set up a small gun safe than have two different long gun-sized secure storage locations.