4" stainless Ruger Security Six, loaded with 158 grain soft lead hollowpoints. Sometimes I switch it out with a S&W model 15-4, but the S&W is currently having light-strike problems and awaiting a tear-down, good cleaning, and spring kit.
I also have a 7.5" Ruger Bisley-Blackhawk in .45 Colt that I would be comfortable with as a HD gun, but I think the double-action 38's are a better choice.