CCW weapons should fit your hand well, should be easily drawn and should effectively stop someone within one or two shots. While size isn't necessarily a concern, one must ensure that the firearm can be concealed properly. Home defense weapons should be easily accessible, easily loaded and easily lockable/unlockable. While they should posses effective stopping power, the fired rounds should not penetrate farther than the walls of your home, if at all possible. While these points seem similar, they can be worlds apart in practice. A 1911 with FMJ rounds is much different than a short barrel 12 gauge with pistol grip and buckshot. Each takes different ammo, each has different recoil, and while each can be effectively concealed, you can imagine how difficult it would be to pull a 12 gauge out from your waistband. Likewise, a FMJ .45 is going to pass through your walls and possibly into the living space of your family. I realize the OP question is 9mm vs. .45cal. There has already been alot of talk about stopping power, lethality, familiarity, etc. Naturally, when you get guns nuts (myself included) in a room, just like hat nuts, there's going to be alot of great opinions and anectdotal evidence. Yet, just as you would discuss the correct hat for a situation, you would take similar considerations for the correct firearm. You were considering a CCW and to reiterate what many have already said, you need to feel these firearms in your hand. You should have ample experience shooting both rounds (9mm-.45). You should pick a weapon based on how well you're able to conceal, draw and fire it. If all is equal, and it rarely is, then you can start worrying about caliber. If you're comfortable firing .45 rounds with reasonable accuracy, then you need not hesitate carrying that round. Do not worry about the versatility of the firearm. Let that be a secondary bonus, rather than a primary concern (i.e. a weapon being effective with CCW and home defense).