There is no "perfect" do-all caliber for everybody or every situation. It all depends on the gun you are able to carry. While most will not dispute the effectiveness of a 45acp, the guns that shoot them are usually a bit large, heavy and bulky and would preclude most of us from carrying one concealed for long periods of time, year round. Small calibers like 22, 25acp, 32acp, 380acp are a bit weak and while there are excellent guns that shoot them (like a Ruger LCP Max) one has to be comfortable carrying a small caliber pistol. I'm not.
So....... the best bang for the size, or size and weight ratio to effectiveness and capacity brings us to the ubiquitous 9mm. 9mm pistols are now micro in size, light weight, carry 11+ rounds on board with a flush magazine and can be controlled by almost anyone. They are quick to reload and have much better manageable recoil than most J Frames. They are affordable as is the ammo for them. 9mm ammo choices are plentiful and it can be gotten anywhere. Given the right ammo choice, the 9mm is quite effective for SD. While the vulnerable 38 special used to be king of the hill, it is now waning due to the wheel guns having limited capacity on board, slow reloading, more bulk, weight and width. Today, the top end 9mm ammo beats the 38 spl's and ammo manufacturer's no longer spend a lot of time and effort improving the 38 special like they do for 9mm ammo. So that would be my summation as to what caliber Id choose for SD, EDC, CCW.