For me .22, good for plinking or target shooting. Definitely good on critters up to woodchuck size for me. Large selection of pellet types. And you can buy them locally in a pinch. You can shoot the heavier .22 pellets to increase your FPE if your gun is capable of launching them fast enough.
When you're talking ammo costs, keep in mind that most tins of .25 caliber ammo have a smaller piece count than a tin of .22 (JSB Jumbo Heavy 18.13gr in .22 is 500 ct, Kings in .25 are 350ct - same price from PA) . Add to that the availability of .25 and the need to pay shipping charges for lead (in my area, no one is selling .25 in a brick and mortar store), the argument against .25 caliber starts to stack up for those on a budget.Number crunching the decision between .22 and .25 aside, I can see the attraction of the larger caliber