The choice of weapon depends on the circumstances......
If I were to keep a gun in the car, it'd be the biggest, most-nickle-plated flashy cannon of a pistol I could find....think about it: There you sit, minding yer own business at a red light with no way out. Three or four approach on foot, they want your car, your money, your wife.......Nothing will state your position on the matter more clearly than when you retrieve that giant nickel plated .357 from the glovebox and sit there with it in your lap. Upon seeing that, I promise you they will leave and seek out an unarmed victim.
For the home.....I opt for the universal sound of impending death: the racking of the shotgun. No matter what language your uninvited guest does or does not speak, nothing says "leave or die" quite like the sound of a shell being racked into grandpa's old Winchester poly-choke.
For personal carry.....I opt for the Keltec .380......be sure to tear that Keltec down the day you get it, deburr the slides and smooth the ramp - or spend the coin on something nicer that's ready to rock right out of the box. The key to this choice is size and weight, dictated by Florida heat. The bottom line is this: If it's too big and heavy, you won't carry it......you'll end up getting beaten with a stick while your 1911 sits useless in your car or in a closet. Be realistic.....the point of carrying that gun in your pocket is not to win a gunfight, it's to buy you enough time to survive, to take cover, to retreat if necessary, to send enough lead downrange to deter the threat. Sounds counterintuitive, I know; but unless you are willing to commit to wearing a shoulder rig or a big pancake holster every single day, you'll eventually begin to not carry. The average joe is not willing to regularly carry enough firepower to outgun some cat who has the element of surprise and possibly superior firepower, whereas a mouse gun will become a regular and faithful companion.......Of course, my dad can rightfully disagree with me because he regularly carries his 1911 in a shoulder rig, old school - if you are willing to do that, I'll concede the point.
On to ammunition.....fragmenting rounds are a great thing. But do you want a fragmenting round in the pistol in your car? No.....It ain't gonna go through the car door like you'd need it to. What about a pistol in the home? Fragmenting makes sense, then. In a panic situation, we are all gonna shoot like ****, do you really want six rounds of hard ammo missing the bad guy, exiting your home, and continuing into your neighbor's house?
These are some additional considerations I thought I'd add. Also, as a FL LEO......I need to remind you that it is sheer foolishness to think we are gonna show up in time to stop the bad guy....I really wish we could, and we love it when we can.......but it's just not reality. We each have a duty to protect our families and our homes to the full extent allowed by law.