If you could have only one handgun, what caliber would you pick?

Trick question. Some handguns shoot multiple calibers. For instance my S&W model 586 revolver will shoot both .38 Special and .357 Magnum. I own a S&W .460 that shoots 3 calibers without changing anything. It shoots the .45 Long Colt., .454 Casull, and the .460 S&W magnum.

If I had to choose only one, it would be my S&W 460V revolver. It has a 5" barrel so its easy to carry but can shoot any of the above calibers. If I am plinking, I shoot the .45LC cowboy. It's low velocity round, almost no recoil. For killing things, even really big things (think Kodiak bears), I will load the .460 Magnum round with a Hornady Custom FTX bullet. Its a 200 grain bullet with 2200 fps muzzle velocity. At 100 yards its still screaming at 1715 fps.

.45 ACP, because it is easier reloading the .45 case than the 9mm.

Carried the standard mod1911 45cal during USCG service. Great sidearm, but I bought a Beretta M84 (Cheetah) for personal use. I liked the open slide design to prevent jams. I wanted a larger magazine (13 rounds). Liked the compact size. Quick field stripping make cleaning easier. Rounds (380) have less power, so I load hollow points.

Hands down the 9mm. The argument about which pistol round is best has been going on since before my grandfather was born. The FBI beat this horse to death about 20 or 25 years ago and came up with the following conclusions:

1) All pistol rounds basically suck.
2) Shot placement matters more than caliber

So when you consider the widespread availability of ammunition, the advances in terminal ballistics of the last 20-30 years (especially in this caliber), the fact that you can get more ammunition in the mag, and better accuracy with smaller shooters... I'll take my 9mm and 10 million rounds and practice, which is the really deciding factor most of the time anyway.