Zero a .25 using FTT' at 10 yards and your are within a pellets width from 6 to 24 yards and it definitely hits harder than all the others I've tried on rats.
Zero a .177 at 35 to 37 yards and you are within "bunny brain" POI from 10 to 40 odd.
That does mean two guns to cover close and far.
I guess if I had to use one then it might, just might, be a .20 but only if rabbits were not on the menu very often and rats were, otherwise...well probably .177
I think and therefore...... I refuse to steal someone else's quote to try to sound more erudite or profound than I actually am.