If you had to choose "just one" defensive pistol, what would it be?

I got asked the following question by email from a writer looking for a Steyr M357-A1 pistol:

I'm still going back and forth between the 357SIG and the 9x19 cartridges, but I appreciate the feedback, very helpful. I thought the 357SIG cartridge would be more reliable in feeding than the 9x19 due to it's signature bottleneck, but I guess time proven beats the hell out of "new technology". The argument is still neutral. If you could have one semi-automatic, autoloading, defensive handgun you could trust with your life in a chosen caliber what would those be and why?

Incidentally, I have already told him finding a Steyr M357-A1 is like trying to locate that elusive mineral, unobtainium. I had one and it was rare when I got it and got so rare it was worth way more than I paid for it, so I sold it. Seemed like a good idea at the time anyway. But back to the question about choosing "just one" defensive pistol. Here's what I replied to that question.

Easy. Only one, my full-size Para P14-45. Ammo is easy to find, reliability is proven, even replacement parts would be available. But that's not an everyday carry pistol for all occasions. For carry I would choose Sig P229 .357 Sig, either of them as I now have two. But you won't go wrong with a good 9mm. Ammo is certainly cheaper and more abundant than .357 Sig and with high-quality hollow points, the ballistics and end results are fairly close to .357 Sig.

 And what I didn't say is what do I really carry more often than any other pistol. Easy again. Kel-Tec PF-9 subcompact with a couple of spare magazines. Fits in the pocket even when I'm wearing shorts.