Well, from an entirely practical point of view, I default to the 50cal. It's cheap to shoot, components to load it are available everywhere, you can shoot anything from 175grain balls right up to 450 grain conicals, and in many guns you can pack from 20 to 150 grains of powder in it (READ YOUR OWNERS MANUAL FOR MAX LOAD RECOMMENDATIONS). This makes it a viable round for just about anything you care to shoot in North America, provided that you adjust your range accordingly. Uh, that means that if you wish to take a grizzly with a .50 that means you have to craw INSIDE his mouth before firing! :rotf:
But seriously, the .50 gives a very good tradeoff between economics and availability. It also gives the shooter a very wide choice of firearms in order to be able to select the firearm that best suits the person carrying it, and it means you can have a light rifle if you wish and also light recoil if you wish.
I guess it's the combination of all the above properties that has led to the .50 also being the single most popular calibre in muzzleloading today. Hmmm, guess I'm not the only one who likes the half-incher... :grin: