Mine would be my .357 Colt trooper with a 6" barrel. Why? It is enough to shoot bigger deer sized animals. Small enough to shoot rabbit sized animals. Will shoot shot shells and low powered 38's. Big enough for self defense. I love reloading these. Numerous sizes of bullets, easy to mold from lead. Uses about any powder known to man.
I thought about a good 22 pistol, but there are too many limitations. So the .357/38 has my vote. I am not dead set on the trooper though, i would go for a S&W, or a Ruger.