I carried a S&W M36 for years, even though I really do not care for the 38 SPL for a defensive round. Got a Ruger SP 101 when they first came out and have used it a lot since. I did carry a Glock M27 and my Glock M21 as well.
A lot depends on the weather and how you dress. When it is snowing and blowing and you are wearing heavy clothing, any one you may get into a shooting with most likely will be as well so you want somthing that will penitrate and still have stopping power no matter if the bullet expands or not. A 45 don't matter, 40 and larger it don't really matter. The 357 packs enough stopping power that it will penitrate well but they have been known to fail to expand when heavy clothing is in the way.
During hot weather or when dressed lightly the smaller package the better. If you get into a SD shooting situation, mag capacity is not as important as where you put the shots, and you want to keep in mind that the average gunfight only is going to last three rounds anyway.
A small revolver, in 357 either five or six shot fills the bill nicely for CCW, and if your worried about running out of ammo three or four loaded speed loaders fit in a pocket very nice as well.
BTW My wife and kids griped for twenty years about not going any place unless I had a gun in my pants, "up my butt" was the way my youngest girl discribed it, I always told them "it went with the badge and handcuffs."