I have maybe 15 or 20 pellet guns. Most of them inexpensive but a few nice ones including a Diana model 48 side lever.
Most of mine are .177 and a few .22. The pellets are cheap enough that I have accumulated more than I will ever use.
The ones I have are fine for small game. Although some models will kill a buffalo, I see no real reason to own one. I will use powder burners for anything above squirrels and rabbits.
Just remember Lewis & Clark used an air rifle in their journey & the first repeater rifle used in battle was an air rifle, used by the Belgium against Naploian & he declared that anyone caught with one was to be immediately killed on sight. there is a copy of it in the NRA mueasem. And when all your powder ammo is gone, us air gunners will still be going strong. And yes there are air guns that can be used on bison,bear,moose,elk,deer & any other game you can think of.