Model 36, IF it's a revolver Im carrying, or maybe a .38 Police Positive Special. Generally tho I would conceal a semi- either a nice Makarov or a 9mm Chinee Tok. Both conceal pretty well, the Tok is flat and snuggles in the small of the back.... The Mak is all around nice but is a bit thick.
Have been known to carry a 4-inch S&W 66 .357 under the back of my pants, but the "hidden" aspect is questionable- likewise with a Combat Commander.
What we carry is either by regulation or personal preference and we learn by trial and error and by DOing.