Licensed concealed carrier here.
Comfort and what you know goes a long way. A .357 would be a good choice for a concealed carry, because of its knockdown power, larger bullet and speed vs the 9mm. However, a revolver is not for everyone. Find a local range that rents out firearms. Go and try out some of them, so that you can see for yourself which fits you the best.
Things to consider:
- Various caliber firearms have advantages and disadvantages.
- Weight
- Size
- Knockdown Power
- Magazine Capacity
- Ammo Price
- Ammo Availability
Only you can decide what is most important to you.
I have three that I carry.
- Smith & Wesson Bodyguard .380
- Beretta Nano 9mm
- North American Firearms .22 Magnum mini revolver
I can carry all three at the same time plus extra mags, which is potentially way more firepower than say a larger high-capacity pistol. All of them are at least 7 round capacity; 20+ rounds at the ready before having to switch mags. Plus it's so much lighter. I use pocket holsters, because they are way more comfortable and I can have my hand in my pocket and at the ready.
Other pistols I no longer own, but used to conceal carry.
- H&K .40
- Springfield XD 9mm
I don't like carrying large firearms unless I know I'm going to be in bear country (currently only the southern-most part of my state). I do not own a pistol that can effectively take down a bear, but I'm typically with friends who do carry the larger pistols when traveling in such areas, so I don't need to own one.
One of my friends obsesses over stopping power and carries a full-sized large caliber pistol with him at all times. I prefer comfort, so a single stack mag 9mm is the biggest I'll go, unless later I get an F&N maybe.
If I were open carrying, it would be a different story. I'd carry a much larger firearm on my hip, because I wouldn't have to conceal it under clothing where comfort is a factor. I would also carry a semi-automatic rifle.
For home defense, I would choose something completely different entirely. A shotgun or rifle with close-quarter combat in mind.
It's all according to your preference really.
After you have your firearm(s), practice is of utmost importance. Go to the range regularly, until you are comfortable with the firearm, are hitting your target and have the muscle memory necessary to use the firearm effectively.
If you have access to an outdoor pistol range, practice speed aiming at multiple targets, mixing it up. This will prepare you for a potential situation. Muscle memory and practice goes a long way toward a positive outcome, if you're ever in a situation where you have to draw your firearm.