IMO perfect answer!The short answer is there is NO perfect weapon for HD or for any situation that involves lethal force. You can not prepare for everything that could happen. Pick a handgun, or shotgun, or rifle that you can hit a target with easily. If that's a double barrel 16 gauge. No problem. If it's a 44 magnum Winchester Model 94. No problem. Any weapon is better than none. This isn't fashion show for the latest tactical accessory out there. Get what works for you. B/C if you're confident and comfortable with the weapon, than you'll do better than something tactical and cool that you're unfamiliar with. Of course if you used an M4 in Iraq that might be your best option. I don't know. You have to decide. As does every individual here what's best for them personally.
Penetration. If bullets don't penetrate they don't kill things. There's no magical way to keep a bullet from penetrating a bad person and not a wall while still being an effective round. Sorry. What ever weapon you decide on using train with it. Don't go spraying rounds all over your house. Tell the kids and wife to lie on the floor if a bad guy breaks in to minimize their exposure. Would it still be possible to do the unthinkable and kill one them with over penetration? Sorry. Yes bullets kill things. On the flip side the bad person with a gun won't be worried about over penetration so taking them out quickly is better I feel. You have to decide what you want to do. Nothing is without risk. Do the best you can to minimize it. I hope you never have to use a weapon to defend your house.
Dave