How much do you want to spend? I've used over thirty different scopes on spring air rifles. I've used BSAs, Leapers, Bushnells, Leupolds, Burris, Swift, Weaver, Simmons, and RWS. I actually WEIGHED each and have specifications of each. I returned the BSAs, Leapers, Bushnell "Sportsman", and Simmons the most frequently.
I had personally rather have GOOD 4-12AO than a cheap 6-24. A pretty good scope for the money is the Swift 4-12AO #676. eabco.com has them. I've had five or six of them and you really can't beat them for the money. They are also rated for use on spring air rifles. Another good scope for the money is the Bushnell Trophy #73-4124 4-12X40AO. I'd recommend either for most scope for the money.
Stepping up in quality is the Weaver V-16 and Bushnell 4200 4-16 and 6-24. You wouldn't regret buying either of these.