12 gauge pump, 38 special revolver

Reasons: reliability, simple design, stopping power, ease of use

If you're forced into defending yourself: for defending a fixed position the 12 gauge will be your friend (except for the recoil!) If you're moving about, the handgun will be easier to maneuver.

If you decide to get a 22, stick with the bolt action rifle and/or the revolver. I've never fired a 22 semi-auto anything that didn't jam on occasion. 22's can of course kill, but they're not generally considered strong defensive weapons. More target shooting and small varmint hunting.

380's are marginal in stopping power in my opinion, and the small semi-autos can be real hand biters (the slide comes back and takes a bite out of your hand, depending on how well you grip certain models).

A 32 combines the worst of the 380 and 22 in my opinion.

For snakes, don't try to do the aiming yourself. Let the snake do the aiming. The ones that like to coil and raise their head off the ground (like rattlesnakes) are quite good at guiding shots right between their eyes. They like to look straight on at a threat. Wave the barrel around a little while pointing it towards the snake, so it interprets the muzzle as a threat. Once the snake locks onto the barrel, all's you have to do it pull the trigger.