I recommend a double-action revolver. It's superior to a semi-auto pistol, or single-action revolver, for the following:
1. You cannot misplace or leave behind a magazine, as you can a semi-auto. All you need for it to function is right there. I remember years ago, driving 30 miles to the nearest gravel pit with my Ruger Mark 1 bull barrel, only to discover I'd left the magazines at home. The Ruger is a terrible single-shot pistol, as the slide has to be held open manually while you try to jiggle a round in the chamber.
2. A revolver will function with a wide variety of ammunition. Want to shoot .22 BB caps or .22 Shorts? The revolver can do it. Not so the semi-auto.
3. Determining if it is loaded, or if you've missed firing a round, is easy: Gently pop the cylinder out the side and look. With a single-action revolver, you have to rotate the cylinder and peer into each chamber individually. With the semi-auto, you have to pop the magazine out and pull the slide back to check.
4. The sights do not move on a revolver, as they do on many semi-autos (the Ruger is an exception, since its bolt moves within the tubular frame). An unchanging sight picture is an advantage, especially for newer shooters. That slide coming back can frighten newcomers, or at the least disturb their aim.
5. Reliability. A well-made revolver will fire with almost absolute certainty every time. Not so the autoloader, which can be finicky on which brand of ammo it prefers to function best.
6. A revolver has no annoying safety to engage, disengage or think about, especially if you must use it for self defense. Granted, a .22 revolver is not the best choice for defense, but it's better than bare fists.
7. Though some would accuse the revolver of wearing out faster, or require more frequent maintenance, I dispute this. I've never heard of a good quality .22 revolver requiring a gunsmith, though thousands of rounds were put through it.
Now, here's what I recommend for a .22 revolver:
a. Good quality, such as Smith & Wesson, Colt or Ruger.
b. 4 or 6-inch barrel
c. Adjustable sights
d. If possible, a spare cylinder for .22 Magnum. This makes it useful for hunters or varminteers.
e. Stainless steel finish, for low maintenance.
f. A good availability of after-market accessories, such as grips or sights.
Well, that's my take on it. Any dissenters?