My preferred caliber depends on whether I am carrying a revolver or a semi-auto. If I am carrying a revolver (out-of-state day trip) it would be 38 Special in my 686+ or 44 Special in a 629, both being 3". If I am carrying a semi-auto (extended length trips), it would be 9mm (P365) followed by 45 ACP (Ruger SR1911CMD). Once my Glock 23.5 comes in, the 40 S&W could displace the 45 ACP, only because I would rather have a reliable lesser expensive handgun seized if I had to use it than some of my more expensive ones.
Note: in my state, carrying loaded magazines is considered a felony, so every magazine has to be unloaded, especially since magazines are part of the firearm. Meanwhile, since speedstrips and speedloaders are NOT part of a revolver, they can remain loaded!