[TranterUK]

I would have to go with the .38, especially if a hollow point, the expansion of the projectile would create a much larger temporary and permanent wound cavity than a .22, and thus have more effect. (non +P .38 HP typically expands to +/-.5" with 10"-15" into ballistic gel).

It is also true multiple strikes, even with a .22 will have a disproportionate effect on the attacker. Thus I would say two or three .22 hits are likely to have much more effect than a single .38.

It should be kept in mind however different people have reacted very differently when shot. Some will take a light flesh wound and roll around crying while others will take several serious hits and still have the where with all to continue. So I dont think there can be a golden rule. Just focus and what ever you shoot remember, only hits count.