most popular with LEO's is a S&W 5 shot Chief Special...leter versions such as a bodyguard or centenial with built in hammer shroud as not to catch the hammer on something.
Speer Gold Dot 38 Special short barrel load is very popular.
Usually the same revolver they use as a back up gun on-duty.
Seecamp 32acp DAO stainless has all been popular...but pricey and limited availability. Nice little reliable pistol. OK with Gold Dot Rounds.
Revolver advantage is being able to fire repeated shots from within a pocket without jamming like an autoloader .