I live in an RV inside a recreational vehicle resort and have a lot of things to think about when it comes to home defense. First off, there are other thin skinned RVs all around us and penetration is even more of a consideration than in a common neighborhood.
Add that to the fact that just down the street last night, a 24 year old woman was murdered (by bludgeon) along with her infant son. The two innocents were brutally murdered and anyone exhibiting that kind of anger demands a weapon that's equally nasty as a counterforce. It makes you doubly think about defense, especially when I have a wife and small dog to worry about, too. Not being a wealthy man, I have few choices, in that this is a "come as you are" type of thing.
I have 2 long guns that could be used, but they were discounted out of hand right away. The .22 Winchester is out for obvious reasons, not the least of which is that even a carbine length longarm is too long inside a Class-A, ditto for my 18 1/2" Remington 870. So, for us, it's the handgun.
Choices are: 6" Colt Trooper MKIII .357, S&W 2 1/2" 686 Plus (.357 Magnum), and Sig-Sauer P-226 in 9mm.
I eventually chose the S&W. The .357 may have more penetration than the 9mm, but the short barrel mitigates velocity. The Colt is too long in the barrel and has near maximum velocity with the .357 due to its 6" barrel-more penetration than the snubby Smith. I need compactness, a hard-hitting, thumpin' caliber and good capacity. The Sig might take at least a double-tap, due to the 9mm caliber, and the less rounds the better in an RV. The reason I had to choose only 1 gun is that RVs are essentially vehicles and RVs get broken into with more regularity than a house. There are also fewer hiding places for a weapon cache, so my "extras" are stored securely locked up offsite.
I chose the S&W as the house gun after I shot it against a S&W 9mm M&P compact and there was no comparison. The .357 smacked the targets (chunks of sawn lumber) with authority, sending the pieces rocketing off into the scrub brush. The 9mm zipped through the wood and the target just fell over after being hit. Both guns used hollowpoints. When you have 7 rounds vice 16 rounds, you want a bullet that hits like a hammer. Because the Smith is compact, I can also conceal carry it away from the rig.
Every HD scenario has its good and bad points. You have to weigh everything and have good, well thought out reasons for choosing the gun you settle on to defend you and yours.
The horrible events of last night serve to reinforce that your desire to have protection is a good choice and anything can happen to destroy lives. Either down the street or right inside your front door. Give HD a lot of careful thought, then act on your solutions.