For me, there is no doubt: my Glock 19. If I could only have one pistol, it would be primarily for personal defense. My G19 has seen me through good times and bad, in all kinds of weather. It is big enough for serious work, yet small enough to conceal easily. And with modern 9mm ammo it will do its job, if I do mine.
There are a lot of other handguns in my safe, but the Glock would be the "one" if I couldn't have more than one.
I have to agree with AuburnFootball the Glock 19. I just purchased one and love it. I went back and forth with a couple of others but, the Glock 19 was the one for me. I also ahve a para ordiance p13 but to big to conceal with lighter clothing.
I hate these what if you could only have "1" questions. Makes me crazy. I love the 1911's and have my favorites, I love the 45 ACP as my favorite defense cartridge. But as far as ONE GUN, it would have to be powerful enough for defense, large enough to shoot comfortably, be able to serve as a service type pistol for open carry, and small enough for concealed carry in all weather, and have a magazine capacity to handle ALL situations. If it comes down to your ONE DAMN GUN QUESTION, I'd say the Glock 19 or Glock 30. No wait..... Maybe a Colt Commander or Kimber CDP 4", or a, aw hell........:
I would have to have something concealable, not just concealable but easy to carry.
If I'm wearing sweat shorts (or had to carry with no jacket and a tucked in shirt) can I carry it in a Smartcarry?
Must have acceptable capacity (subjective) and stopping power.
Night sights are required.
Glock 27 or Springfield XD 40 subcompact: 9 + 1 of 40 S&W in a concealable, user friendly package.