.22 or .25

As others have said, if you are shooting anything bigger than a possum then .25 is the way to go if NOT .22 ALL DAY. I own a Lelya in .22 and my Leshiy just arrived also in .22, my FX IMPACT MKII is also .22, i shoot STARLINGS and Pigeons 90% of the time but if i ever had to take down a raccoon i could swap the barrel on the Impact or the Leshiy to .25 and go from there.
 
The question is less .22 or .25 caliber preference, but more which seems best in that platform. Your limited on power due to the shorter barrel and likely air too with the cylinder. So I would say a .22. Decent amount of shots and better velocities for trajectory.
honestly between a 22 and 25 out to 100 yds trajectory and wind drift are very similar if velocities are the same. But a faster flatter 22 will hold up better than a slower 25.
 
How's your dexterity? I don't shoot 177,well I prefer to shoot 22 over 177 simply because it is easier to grip and load the 22s. Once you get further along in age or injuries or both this becomes a factor. I believe the 22 is the more common or is becoming the universal caliber for air-rifles. It use to be only the 177, never heard nor knew of another air rifle caliber back in the day that was not a 177. lol that's been awhile ago. Competition being the acception for now but from what I see this is changing to 22. I know from exp that the 22 will end any problems with Mr Skunk, Possum, Raccoon,or Squirrel at the distance you present. If I were to use a 25 caliber implement I myself would have concerns along the lines of pellet down range distance & energy. Please try and test a variety of pellets to determine which pellet is most accurate and effective for your tool of choice before you elliminate said pest . Best of luck