For me, it's the Shadow 1000, hands down -though I don't own one anymore, having given mine to my brother-in-law as a kind of present.
Here in California, all resident small game species may be taken by licensed hunters during open seasons with air rifles. This includes resident game birds, such as quail and chukar partridge. For chasing chukar and quail across the often steep and nearly always rugged country of California's High Desert environs, it is hard to imagine a more ideal rifle than the Shadow 1000.
First off, it is one of the lightest spring-piston air rifles on the market at about 6.5 lbs, sans scope and mounts. It is no slouch in the power department, hitting 16 ft/lbs+ at 5,500' in elevation with a variety of ammo types. This level of power in .177 translates into a trajectory that is flat enough to allow for a maximum point blank range of 50 yards, assuming a 1" kill zone.
My wife liked the one that I had so much that she insisted on getting one of her own, which we still have in our household. Both were satisfyingly accurate.
While not pretty, the stock of the Shadow is supremely functional, with the textured surface enhanced by panels of bumps or "pimples" which provide for a sure grip in handling.
Yeah, it's a little, uh, "plasticky" compared to an "R-Series" Beeman. But then again, so is a Glock firearm pistol.
The only downside that I have found to the Shadows is in the trigger. The 4.25 pound pull isn't totally unmangeable in the field, but the inconsistant letoff can be disconcerting to some. One plus of this, however, is that not knowing exactly when the sear will trip sort of forced one to follow through with the sights after the shot is loosed.....
I could go on and on..... I like the silent and intellegently placed safety that can be engaged and disengaged without recocking. I like the low cocking effort that feels lighter than the advertised 38 pounds compared to my R-9's that feel every bit of their 40.
While I do prefer to hunt with my .20 R-9, much of that has to do with the caliber and aesthetics, the latter of which a rabbit, quail, or chukar could care less about.
For the hunting that I do the most of, the Gamo Shadow is a good choice. Mine served me well while I had it, and continues to take game in my brother-in-law's hands. I expect I'll be buying another, someday.
If it came in .20, there would be no hesitation!
-JP