The world of air rifles can be a lesson in frustration. The ones really into it go so far as to buy pellet sizers, weigh their pellets, and the list goes on and on. For a decent, accurate, mid-range rifle look at the Diana 45 if your main focus is varmints. If you expect more, save your money, do some research, and buy the best rifle your money can buy. Just remember accuracy standards for an air rifle is 33 feet (10 meters) Beyond that it's a **** shoot.
Another thing to remember. With spring piston type air rifles if you are going to scope it, you MUST use an air rifle grade scope. I have seen these guns shake the guts smooth out of Leupold and similar quality scopes in a matter of a few shots.