You should at least consider the Bushnell Elite 4200 (formerly B & L). Optically and mechanically it is at least as good as a Leupold; plus, the air rifle distances are indicated on the adjustable objective, so there is NO GUESSING when you're focussing for your next animal. It comes from the factory with a target dot (1/4 minute, I believe). Adjustable from 6 to 24x. The only downside (besides the 1/8 minute adjustment, which you may or may not find annoying) is the weight (about 21 ounces). But on an air rifle, weight is usually not an issue.
And, they cost half of what a Leupold does (under $400 if you shop around).