The most important thing about a pistol purchase is to think about what you will use it for. If your primary concern is home invasion or family protection in a dark/confusing situation you need a revolver.
Caliber/power/recoil/muzzle energy/hole size/penetration.... blah blah blah. They mean nothing when the SHTF. You need to be able to hit something before you worry about how big a hole you are putting in it.
Go to a gun show. Pick up some guns. Hold them.
Go to a shooting range. Rent as many different guns as you can. Shoot, shoot, shoot.
Take a basic pistol class. Find an instructor like Semper to run you through drills.
Get some snap caps and practice failure drills.
The best way to find out how your gun works is to learn to disassemble and clean it and put it back together. Have a knowledgeable gun owner or smith show you how and do it over and over.
Finally, pray that you will never, ever have to put a hole in a person. Read as much as you can about real-life gunfights, active-shooter scenarios, and personal assaults.
Prepare yourself mentally for the possibility that you will end a life. Consider it deeply and talk to soldiers/Marines/cops who have had to do it.
After all that is said and done, it doesn't make a damn how many millimeters your bullet is or how many cartridges your magazine holds. Pulling a trigger and hitting a human being will change any preconceived notion you have about gun ownership.
I am not saying any of this to scare anyone or detract them from gun ownership. Firearms are a tool and if you don't know what you are doing (by heart, automatically, every time) someone will get killed. Handguns are made to kill living beings and they are very efficient at that.
Jeff Cooper has the best gun safety rules:
RULE I: ALL GUNS ARE ALWAYS LOADED
RULE II: NEVER LET THE MUZZLE COVER ANYTHING YOU ARE NOT WILLING TO DESTROY (people, pets, neighbors)
RULE III: KEEP YOUR FINGER OFF THE TRIGGER UNTIL YOUR SIGHTS ARE ON THE TARGET
RULE IV: BE SURE OF YOUR TARGET AND WHAT IS BEHIND/BEYOND IT.
As far as advice on gun choice - You simply cannot go wrong with a Smith and Wesson .357 revolver. I sold my 686 last month after 15 years and I kick myself every day. You can go to the range and shoot cheap .38 SPL all day and it won't wear your wrist out and you can come home, load it with .38 +P or .357, store it safely and you are ready to go. Misfire? Pull the trigger again.
I do NOT recommend Glocks for a first time shooter. Glocks are probably the most successful autoloader in modern history and they have a well-deserved reputation. In the hands of an expert they are unstoppable. The problem with a Glock is no manual safety. This is no problem for an experienced shooter but a new gun owner that has not learn to keep their finger off the trigger could have problems.
You can throw a loaded Glock off a building and it won't fire but if you pull the trigger it will.
So (finally) "power" is the very last thing to consider in a pistol. When you have shot a dozen different models and calibers, know what you like and don't like, and are able to handle it automatically and without hesitation THEN you can worry about ballistics.
