I'm not trying to be a smart guy here... the best scope you can afford! That's basically what it boils down to. There are so many great scopes available ranging from crap to inexpensive but very high quality, Discovery Optics, Vortex, Sightron, Athlon, Bushnell, Nikon, Leupold, Nightforce, all the way up to Schmidt and Bender scopes in the $3000+ price range. It all boils down to how much you can spend. Many suggest you pay at least half the amount you paid for your air gun on a scope. If you can afford it, pay more than that. Quality optics are often overlooked but are an extremely important piece of kit. I think if you give an amount you're willing to spend, you'll get many suggestions of scopes that will serve you well.
I have Discovery scopes in the $275 price range that is phenomenal for the money. I also have an Athlon Ares that is excellent. I also love the Vortex Diamondback Tactical line. I own many Leupold Optics and have always loved them too. I don't own any SWFA scopes but they are quality ad have a huge following too. Probably forgetting some but like I said, give us an amount you're willing to spend and many people will chime in with great options.
Good luck. Stoti