For me, hands down, the .357. I like them all and I own revolvers in a half dozen different calibers. But my faviorite is the .357 and it is proven out in the number of guns I own in that caliber. The caliber itself is part of the equation. As was mentioned, you can shoot anything from plastic bullets from Speer, on up to bullets weighing in the neighborhood of 200 grains. It is a great plinker, hunter, or personal protection piece. But for me I think the best part of it is the package. There are so many great guns chambered in this caliber and as mentioned they vary from pocket pieces to large frames. I have a little SP101 that I can drop in my pants pocket. I also have two Redhawks in .357 that take two men and a boy to hold up. The Model 19/66 is the perfect belt gun for defense.......................... Back when the .357 was introduced, it was considered to be a very potent cartridge. Wesson hunted all over North America with a .357 and took animals up to and including grizzly bear and moose. Nothing has changed about the cartridge, it is still just as potent as ever, but our attitudes have changed to believe that we need a .475 Linebaugh or a .500 S&W to take a 150 pound whitetail deer.