I've done so much research on scopes lately I have analysis paralysis. The number of brands and options leaves a person dizzy. I also struggle with finding an optimum scope magnification as it relates to airguns, and have come to some conclusions during my quest. The first question to ask is, what do you intend to use the scope for? If you're mostly bench/target shooting, then higher mag seems to be favored. Allows you to really "zone in" on punching the bullseye, and you don't need a large FOV for target shooting. I think 5-25 and 6-24 are popular but I don't shoot bench so not sure what people are using. If you want to use your airgun for close range (less than 50 yards) pest control then a 2.5-10 or 3-12 should work fine. If your pesting out to 100 yards, then a 3-15, 4-16, or 3-18 should work well. For me, the 3-18 covers a nice range for most pesting applications. These are my opinions of course based on experiences.
Why 15-18x power for pesting? Take a quarter out your pocket and set it 100 yards away. This is your kill zone on most small critters. Now look at the quarter on 9x power, then look at it on 18x power. You will quickly see why some airgun enthusiasts prefer the higher power scopes. Similarly, you won't want to use 18x mag on a target only 10-15 yards away. For close range you'll need to dial back down to 3-4x mag for those shots.
Hope this helps.