You are about to be bombarded by a lot of opinion and a few facts. The truth is, ANY premium JHP round in 9mm or larger will likely do the job. (At least as well as a handgun can be expected to do the job. Handguns are emergency weapons we resort to because they are easily portable and concealable.)
In the last day or so, an expert, Massad F. Ayoob, posted the following in response to the never-ending debate about some of the standardized tests for stopping power.
"Anyone who has a "crisis of confidence" in their equipment due to the "IWBA versus M&S debate" can simply choose a "load of compromise," something both sides agree works well. That would include the 158 grain lead hollowpoint +P in .38 Special, and the better 180 grain .40 S&W and 230 grain .45 ACP JHP loads."
We love to argue over 9mm vs .45, JHP vs hardball (FMJ) ammo, and try to outsmart each other, but in the real world, you need to use the gun and cartridge that you shoot best. When you are fighting for your life, you need all the advantages you can get, and it doesn't matter how good the bullet is if you don't hit with it.
You need to go to a shop that rents handguns and try a LOT of different guns. You will find a surprising number of options and schools of thought. I'm going to recommend that you try a Glock, a .38/.357 revolver, a good 1911, and a variety of modern autos like the M&P, the XD, the H&Ks, etc. You may be surprised to see that larger calibers aren't impossible to control, and that heavier, longer guns are easier to shoot. You may have a completely different opinion when you leave than when you walked in.
I have carried Sig, Beretta, Glock, Taurus, S&W, Para-Ordnance, and a few others, but I came home to a 1911. It's what I shoot best. You also need to realize that you may settle on something, but over time, you change your mind. This is certainly allowed. Just because you pick something now doesn't mean you are married to it.
I usually steer rookies to Glocks. They are capable of doing any mission for any force in the world, and have been well-proven. They are less expensive, and they are one pistol I will confidently buy used. They aren't too complicated either. I carry a full-size 1911 in .45 and I use 230 grain HSTs which consistently expand to the size of a quarter. I think that there is no reason not to carry the biggest, nastiest round I can shoot well.
Bottom line, if you get bombarded with advice from us, your uncle the retired security guard, your friend from high school who knows a lot about guns, and gun shop owners, and we are all telling you one thing, but YOUR GUT TELLS YOU SOMETHING ELSE, GO WITH YOUR GUT. It's not our *ss that's on the line here, it's yours. Read and train. Treat this as an ongoing life experience that never ends. You are never done training and deciding.