Revolver or semi-auto? Which caliber? Which make and model? What ammo capacity? There are many considerations. It can easily become overwhelming and result in "analysis paralysis."
It's possible that you'll go through several guns before you settle on your perfect sidearm. But if you're the type of person who just wants to make one simple selection that will serve you forever, and you don't plan to become a gun nerd or collector, just buy a small to medium size revolver in .38 caliber.
This configuration is easy to shoot, highly reliable, and requires little to no maintenance. It doesn't give you the high ammo capacity of more modern handguns, such as the tiny Glocks, but it also doesn't pose a risk of malfunctions during a high-stress moment. All things being equal, simple is better when your life is on the line.
And as an additional benefit, some experts believe that older style firearms are considered less "threatening" and more "normal" to a jury who may consist of community members with little or no firearm experience. They can generally see themselves owning a simple revolver when they can't see themselves owning a super-duper high-tech black tactical pistol with a laser sight and customized grips.