I agree with most of what has been said already about the .22 caliber, but AK73 hits the nail right on the head regarding .177: flatter trajectory, cheaper ammo, and will do the job if you do your part. Don't forget, you're looking at a PCP, not a springer. You can sling the really heavy .177s and not see much appreciable change in your trajectory (I think I saw 16 grain .177 pellets on the Pyramyd Air website the other day). I've smashed big woodchucks with my .177 Benji Trail by hitting them in the fuse box. I've also watched them stumble away injured as I fumbled to reload because I blew the shot (in .177 AND .22). A Disco is pretty powerful for an entry level PCP, and mine in .22 shoots pretty darned flat with the right pellet (and at reasonable ranges). But a .177 may yield a higher shot count, and could be more accurate at greater distances? Bigger is not automatically better, just scan youtube for some of the European guys hunting vids. They're doing "lights-out" one-shot kills on squirrel and rabbit with 12 foot pound .177 guns! They just use proper shot placement to do it.