First and foremost, I'm looking for stopping power (which would definitely have to be the .45 caliber) but at the same time compact enough for everyday concealed carry.
Speaking from personal experience, a
Glock 20 works fine for me. At 5' 6" and ~150 lbs, I'm not a giant but find the full size pistol works fine. The key for most concealed carry guns is not so much the size of the gun but, how you
carry it. An accessible mousegun is better then a elephant gun you can't access in a timely manner or use effectively. If I were in the market today, I would probably opt for the full size 357 Sig.
Spend some money on a GREAT holster! In my case, I used several different models for a couple of weeks until I struck gold with a Bianchi PDQ model. I carried this way for several years in Texas and never once was spotted or singled out by a waiter at a restaraunt, clerk at store, etc. unlike some of my friends carrying smaller guns.
Stopping power is very subjective thing. How much penetration do you want? How much bullet mass? How much cross section or sectional density? The 10mm is a great combination of BIG and SLOW versus SMALL and FAST schools of thought. In the environment I live in today, I favor more range and deeper penetration so, based on real world use data from law enforcement agencies I am opting for the 357Sig. The 357 Magnum in 125gr hollowpoint is a proven round which serves to further validate the 357Sig since the ballistics are so close. Texas DPS switched from the SIG P220 in 45ACP to the P229 in 357Sig based on real world conditions civilians are apt to encounter in today's environment, NOT storming a beach 55 years ago or at a shootout outside a saloon in some dusty lawless town of the old west.
If you want a small gun, the Glock 33 in 357Sig still manages good ballistics from its short spout but, a G31 with it's longer tube will serve you better with its longer sight radius and additional mass.
Buy a gun you can shoot well. A solid hit from a
weak 9mm is better then a miss from a
strong 45ACP.