I'll go with a convertible Double Nine. Nine rounds of .22LR or .22WMR in a double action revolver is a hard thing to beat. The only improvement I could imagine would be a slightly longer barrel, like maybe 7-7 1/2 inches.
I'm glad not to be constrained by this thread. I have a Buckmark Camper, a Browning Challenger III and two Rugers MkII, one in stainless and one blued. All have 5.5 inch bull barrels except the Challenger which is slab sided. Nothing for sale.
The Ruger Bearcat that I bought my 11 year old. Vary impressed with it. Solid and will last a lifetime. Small enough to slide down your front pants pocket.