small = .22 rimfire-that's a given, got a Marlin 881, walnut, tube mag. w/4x32.
Meium = .270 Win., got a Savage Sierra110FM w/4-12x50AO.
Large = .30-06 Springfield, tried and proven. Don't have one, need one.
With the rimfire being like needing air, my choice for small would be .223, cheap, easy, and accurate to shoot. Probably an AR.
With the .270 the '06 is moot, so maybe the .50BMG would fill that void?(God Bless John Moses Browning.)
Just depends on what I need to do. I mean if it is just to reduce unwanted critters, does it matter how dead they are?-use the .270.