5 inch
the 5 inch was used by S&W long ago and later reduced to 4 for uniformed holster carry..the 5 is a fine length...not so awkward to wear as a 6, but with more sight plane and more weight forward than the 4. some of the grand old pisolteros, like skeeter skelton, were fans of the 5 inch revolvers.
if going to carry a revolver as an officer the 4 inch probably still good choice for all day, everyday, in and out carry...but for general civilian use the 5 inch is an excellent choice. (holsters..now, a holster...that may be another issue for a while)....