I use a bushnell banner 4-12 on most of the airguns ive had also so do many other shooters it seems the scope of choice and price point really, it is currently sitting on a 22 now.
The manufacturer states they are fine for spring air rifles. THey run about $120 and you can find them on the EE quite often. For the money they are nice and clear even in low condiitons. Anyways its a bushnell so if it breaks you just put it in the mail.
Currently i am using a tasco bantam 4x20mm with circle reticle $20 at michigan walmart.
Im really impressed that its holding up for the last year with no problems.
Also tasco, rex, most companies make airgun scopes
IF you have a more specific question let me know
IanC