I chose the G27 because I realized that is was about the same size as most of the sub compacts out there. As a matter of fact, you have to get into the Ruger LCP / Keltec P3AT / Diamondback .380 size guns to go substantially smaller.
I also realized that other than during winter coat season, I'd have to wear some kind of shoulder rig or an holster as this is not a "slip in the pocket and forget its there" gun. None of them in that size are. (unless you have huge pockets!)
So since I started out with a G22, I figured I'd keep my calibers together - a .40 for the house and a .40 for the car.
that way I can stock up on a single caliber and if I had to walk off with my stuff I only need to bring one caliber.
It would be hard to have to leave stuff behind just because you can't carry another 1000 rounds for that caliber and it wouldn't make sense to take it with you if you didn't take ammo.
I'm not, however, a .40 snob. I have the 9mm drop in barrels for both guns and they'll use the factory mags all the way up to the G18, 33 round, magazines. It's like having at least two guns for the price of one.
I don't have the G23, yet, but it's on my list. I actually like the idea of the G23 with the MechTech carbine conversion kit.
- now that's cool I don't care who you are. . .
The MechTech folks have stuff for the 1911 as well.
I say"Everyone should select a favorite caliber and buy all the Glocks in that configuration! It'll make you happy if you do!