really depends on what your looking for:
Spring Break barrel single shot/ Nitro Piston Break Barrel Single Shot/ or the more extensive and "expensive" pre charged Pneumatic rotary clip multishot Rifle
Price range is the next issue... then...-if you want a varmint grade air rifle there will be some needed fine tuning.
Lastly the spring rifles shoot differently from the pneumatics due to the vibrations of the spring shooting forward when the trigger breaks.
Pneumatics for the most part have a consistent break and projectile alignment producing the best target grade accuracy potential.
If your looking for a rifle with the recomended power levels that would humanely take small game out to distances within 50 yards, your looking at a high end break barrel or a pnuematic in my opinion.
The Benjamin Nitro piston rifle is one example- going for around 275.00 give or take.
They have a .25 cal version that gives you close to 25 foot pounds- enough for close range shots under 50 yards.
Pneumatics are going to be more suitable for shots taken farther than 50 yards because ya just loose too much energy at distances. Your looking at 30-70 foot pounds which is a different realm in terms of power.
Great youtube sites to look at reviews would be "Pyramyd Air, or Ted's Hold Over" These 2 will give you a great overview of the pros and cons of a few brands.
I've shot a few pellet rifles in my days and my conclusion which came recently was using the CCI Quiet ammo out of my 1022. ( 40 grain solids @ 710 fps) Out of the 18.5 inch barrel it produces decipel levels of a high power pellet rifle and I get a tad more than 40 foot pounds at the muzzle. At 50 yards I've produced 5 shot groupings 1 & 1/4th inches which is enough accuracy for my hunting needs. Much more accurate than CB longs and shorts.
I get these for around 3 bucks a box of 50 and they seem to work great for me
-when I found out I could turn my .22lr into an accurate pellet rifle