Early in my study of firearms, I read somewhere that you could conceivably hunt any animal in north america with a 12 gauge shotgun. At first I thought, "wow!", but then I realized you could hunt any animal in NA with a primitive bow and a flint-tipped arrow. The Indians did it for years.
So, I'm going to say that my most-practical all-around gun is my Sharps rifle chambered for 45-70.
Here are some reasons:
-- No animal is too big. It will handle hotdog loads that have been used for hunting the big 6 in Africa, and handle them with grace (not as much recoil as I expected).
--No animal is too small. You can hunt squirrels by "barking" them, or you can put in a "forager" round, which is a brass shotshell about the size of a .410
--It can handle black powder rounds as well as smokeless.
-- With a black powder blank and a line throwing projectile, it can send a 140 lb. test nylon line up to 1,000 feet. This has rescue, marine, and industrial applications.
-- With a black powder blank, it can fire an arrow. This must have some application.
-- It is reliable, just like the field mark on the barrel says.
and, the number one reason why it's the most practical firearm I own......
--Because it's the one I'm most familiar with.