I'm all about the soul of the weapon, not the caliber - I firmly believe that a .22lr through the eye socket in under a second will beat a .45acp in the foot. For that reason, the first thing I look at is the reputation of the specific weapon and its manufacturer. If these both meet my requirements, I'll look at the weapon as a candidate for my teotwawki cache.
For example, I bought a SA loaded 1911 that turned out to be a POS. The rep of the weapon is great, but the manufacturer seems to have problems. I learned my lesson, here.
Then I bought a Colt 1991, b/c I "needed" it for work. I got a great deal on this pistol so I really couldn't pass it up. Even if it had needed work, I would have come out cheaper than buying new and modifying. Great weapon in a great caliber.
Most recently, I bought a Browning High Power. The 9mm Luger/Parabellum is a lightweight in the cartridge world, but there are plenty of them in the handle. The weapon feels great in the hand and balances very well. The natural-point characteristics of the design more than make up for the small caliber. That and the fact that it's a weapon that would easily work for my mom or girlfriend.
My next purchase is going to be either a Colt Trooper MkIII or a S&W 686. Shooting .38spl rounds, these ladies recoil very little. Either one points great and has a wonderful trigger.
Above all, how does the weapon strike you? That's my first question. When I look at a Glock, for all their reliability and such, they just don't make me want to pick them up and fondle them. If I absolutely needed a gun that I wasn't going to worry about, like a dedicated truck gun, a Glock might be the ticket. However, once you've looked into the deep, rich blueing on my BHP, going with a Glock just doesn't seem to be an option.
The Samurai sword is absolutely functional....but that didn't stop them from being made into works of art that the Samurai could carry with pride.
To each his own. I prefer to be fast enough to put the bullets on target with all due speed. The size of the bullet does not matter.