No contest. The 38 Special is far far away the most popular revolver caliber ever. Ask any shop owner that sells ammunition or reloading equipment for confirmation. If I were buying a revolver today it would be a 357 but 90% of the ammo fired in it would be 38 Special. I shoot a lot of 22 LR, 9 Parabellum, 45 ACP, and 38 Super but mostly in semi autos. My concealed carry gun is a S&W model 60 in 357 Magnum and take it the range regularly but more often than not shoot 38 Specials in it. I own and know many others who have progressive reloading machines setup for 38 Special. No one that I know has a progressive loader set up for the 357. Go to any IDPA or NRA Action Pistol match and competitors shooting revolvers are almost always shooting 38 Specials. Go to the NRA National Pistol Championships and see the revolvers in the Distinguished Pistol and Harry Reeves matches, again the 38 Special is dominate. Go to your local range and see what most shooters are shooting. Again, the 38 Special is dominate. I teach concealed handgun classes and some students qualify with revolvers, virtually always shooting 38 Special ammunition. When I go hunting I carry a S&W 29 and I shoot 100 rounds a year through it but I may shoot 5,000 rounds of 38 Special a year. The 38 Special is the most popular revolver cartridge ever designed.