I have owned dozens of handguns. About five years ago, I decided that, to simplify maintenance and the number of spare parts and tools that I need to keep in stock, I would be going with one brand of handgun. I wanted it to be striker fired, available in multiple calibers, and relatively common as well as reliable.
I arrived at this decision because I had just gone through dealing with my 1911 phase. I owned several 1911 type handguns: Several Kimbers, a Colt, and a couple of others. They all required more maintenance and were less reliable than any other category of handgun that I owned. They became safe queens. For more than a kilobuck, I expected more. Sure, you can get a reliable 1911, but expect to spend as much on one as you would on a machine gun. I decided that I wanted to find something more reliable.
Then I realized that there really was no difference between handgun cartridges. The 45 versus 9mm versus 40 debate just stopped being interesting. For all practical purposes, there is no difference between handgun cartridges. So, I gave up on stocking so many different types of ammo.
I sold many of my own handguns and thereafter decided to buy firearms based upon the niche they were to fill. The Smith and Wesson M&P series fills most of my needs. I have full sized models in 9mm, 22LR, and 40 caliber. They all even have the same sights on them (Trijicon HD in orange) so it is easier to transition from one to the other. I also have a 357Sig and 9mm barrel for the 40, so I can choose my caliber.
For those times when a single stack is needed, the Shield fits that bill nicely. Again, the Trijicon sights make transition from one handgun to the other easier.
I also have a Jframe, just so I have a handgun that I can quickly slip into a pocket for a quick trip to the store. I am also planning on getting an M&P 9mm compact just in case the legislature finally decides that teachers can be accepted into the Guardian program.