Pellet design is worth more than caliber, in my opinion. Testing in different mediums, all calibers penetrate about the same. Shock increased with size (same pellet design) as expected. A .30 will produce 100 fpe, and a .22 LR is 120 fpe; I feel there comes the point that if you want long-range, then use the tool best suited for that.
Pellets that are pointed or round produce low resistance and low shock. Blunt pellets have more knockdown with nose design, causing the tissue to deflect in different directions resulting in damage accordingly. Expansion is overrated in airguns!
For me, I like a .177 for squirrels: smaller holes and minor damage for body shots. I don't like bloodshot meat or bone fragments in my dinner. I aim for headshots, but sometimes you have to take what you can get within reason.
I have purchased a .25 and .30 for something different. Mainly for the ol' big and slow large caliber hunting. Old single rifles and rounds of the good ol' days are too difficult to come by, but pellet rifle might just fit the bill.
Happy hunting