I hear a lot of talk about caliber in choosing a CCW gun - or comfort in Carrying. But I think before those considerations there are others more important, in fact, crucial. Here are mine:
In general: Pick the gun you could still shoot effectively on the worst shooting day of your life. In a life and death emergency it may well be.
Start with highly reliable guns. Then:
First, you have to be able to get to your gun under various clothing you may wear, more than just a T-shirt. You may have on a coat, and under that a suitcoat, for example. So, size of the gun or hilt can be a factor as is your ability to grasp it quickly and firmly with clothing a factor.
Second you have to be able to draw that gun FAST, present it FAST and shoot it accurately FAST, maybe a couple of seconds. A gun can be too large for you to handle well - or too small -
Third, you have to be able to shoot multiple times, quickly and accurately. So, recoil and the way you can handle that in a perspective gun comes into play and how easily you can shoot it with accuracy.
After a good period of practice, out of those guns you can do all the above with with ease, pick the greatest caliber.
Out of all those, pick the one that feels most comfortable carrying in concealment.
(If it's impossible to conceal the gun, well, start again with another. Keep in mind though you can sometimes find ways to conceal a great SD gun by dressing for it or by choosing a holster that makes it possible.)
So, my .357 Colt Python, while it WOULD be great for SD, and may be for SOMEONE ELSE, isn't for ME, because while I can shoot it well at the range, I can't draw it anywhere near as fast as others I have with my small hands and it's big hilt. Plus, even with a good holster, it's bulk and weight get to me carrying it. Too bad, but that is the reality.
I think the reality of what may happen in an emergency - being thrown off what can work at a range - means you have to examine the needs of an emergency when you may well not shoot your best or fumble the draw - or find that tiny gun that is so comfortable to carry you now can't even locate quickly as someone runs at you with a knife. A gun that costs $3000 and your friends love won't be good for you if you can't use it well when death stares you in the face.
Anyway, my view for what it's worth.....