After a lot of years and different guns, I found I like revolvers for CC. A few reasons:
1) carries easier, conceals better - the curves and shapes on a small revolver blend more naturally under clothes - nothing "box like" that really pops out at you visually
2) simple manual of arms - draw and shoot. No safeties, no fuss.
3) six rounds is plenty in real life. This isn't the movies, and thorough studies by state and federal agencies have shown most shootings involve less than 3 rounds discharged. So with my revolver I can,
on average, get into two separate self-defense shooting situations in one single day and still probably have a a single round left before I need to reload.
4) more power for the size - .357 in a small package is a hell of a lot of firepower. I like the .357 as a cartridge/chambering. It gives me tremendous versatility with different loadings.
If you don't like revolvers for some reason, no worries, autos work, too. These are my lessons I've learned and what I go by, but there are other theories and plenty of good autos to use as cc guns, and people who prefer them. I'm just sharing my thinking and others can reach their own and practice it. I'm not trying to convert anyone (as a matter of fact, I would prefer it if people would go back to the way it was in the '80s and '90s and just ignore revolvers, letting the prices drop back down to low levels so I can buy 10 or so more wheel-guns affordably
).
As to .357 vs. .40 for a carry cartridge, I would feel fine with either. I think anything above 9mm is, in all reality, a fine choice. I have shot and own/owned .38, .357, 9mm, .40, .44 (special and magnum) and .45 (acp and Long Colt). For cc, I would use any of those calibers without a worry. Hitting where you want is MUCH more important than whether the entry hole is .355" or .454". Heck, if 9mm isn't big enough to kill ya', I guess a .30-06 would barely be noticed, right?