No matter what, you want as much magnification and clarity as you can afford. You'll probably spend most of your time at high magnification. Don't shoot a .204 Ruger, .220 Swift, or my beloved 22-250, because you'll ditch your .223 so fast...
My prairie dog gun is a Model 70 22-250 with an ancient (compared to today's scopes) SFP Leupold 6-20x with Boone and Crockett varmint reticle (works great, it's just another holdover reticle). I really don't miss with this rifle and it's killed a lot of animals.