I agree. Inside the store there is no need for concealment. I'd say a .38 caliber is OK. The cops used to carry that, before they all went to 9mm. However, I'd want more than 6 shots available. That's why I prefer semi-autos. Even a Browning Hi-Power gives you twice the number of shots as does a revolver, and it's a very easy gun to shoot accurately. Other guns give you even more rounds than a Hi-Power. Worth it, in my opinion.
Yes the cops went to the 9mm for the higher capacity but have since recognized that it too is underpowered. Therefore the .40 or .45 is now more standard.