I would suggest a revolver that has ammunition that you can easily find. With a revolver you can shoot mild loads for some purposes and heavy loads for other purposes. With a semiautomatic you have a fairly narrow range of different power ammunition to make the pistol work with reliability.

Long barrels are easier to hit targets with but a real pain to carry around. A 4" barrel works well, a 6" barrel is still manageable but a bit awkward, and anything over that usually stays in the truck.

A 44 Magnum works, as does a 45 Colt. The 45 Colt can be loaded much more heavily if it is used in a Ruger firearm and it can come pretty darn close to the 44 Mag. Ammunition for both cartridges is fairly easy to find.