For most of us average Joe's here in TX that will scratch a whole bunch of great handguns off the list (think full size 1911, or Ber92, or G21 for example). Once you've found one you think you can/will carry everyday/all day then start looking at how well you shoot it, are you satisfied with your ability to hit and the caliber's ability to succeed, and of course the gun's reliability and ruggedness for the task.
For me that pistol is the Glock 27. Reliable, shoots well, has 10 rounds on tap with a 15 round backup mag, and in over 10years of carry I can't get the Glock supplied parts to rust -even worn IWB in the TX summers (something my old Colt Officer's ACP could never endure -it would literally have red spots forming after a day of carry).
I own many other Glocks and carry them often, but the carry gun that covers my worst case scenarios is always a Glock 27
