Double Action Whell Gun (Revolver)
The best thing you can look for, is a revolver from either Smith and Wesson, or Taurus Arms Wheel Gun (Revolver). A revolver will NOT jam, and they are safer to handle when you are EXCITED.
Rest assured, when you are needing to use a gun, you will be excited. The old saying, Keep It Simple is true when it comes to self defense.
I would suggest a .357 magnum, in a revolver like a "Lady Smith" since you can shoot both .38 specials, and .357 out of them. (They are the same diameter bullet, but a magnum is just a longer cartridge, which allows to pack more powder charge.
That way you can shoot .38's for target practice, and fun, while learning, and carry .357 mag. in the gun at all times for defense.
Taurus makes a .357 now, and their quality is just as good as Smith and Wesson.
(As an old timer, believe me, it is hard for me to say ANYTHING is as good as a Smith, but Taurus now makes a hell of a good handgun.)
Automatics can jam, if you wind up with a bad load. With a revolver, if a cartridge doesn't fire, then you can just pull the trigger again. An automatic Glock doesn't allow for that. If you are excited, and it jams, you are screwed.
If you keep pulling the trigger on a revolver, you are guaranteed to get a round off without jamming.