I've never loaded the .357s but hear they are a pain in the watusi due to the short neck.

I like some bottlenecks due to their history, such as the .32-20, .38-40, .44-40s, and even the .30 Mauser, and would like to get into the .25NAA, .32NAA or 9mm AE just for their uniqueness. But to me the .357 Sig has nothing to offer over the .40 S&W. They may be more reliable, but I've never had any kind of reliability issues with any of my .40s.

The main attributes to look for in a defensive cartridge is expansion and penetration and going to a lighter and smaller bullet is only a step backwards. If I were going to use it for hunting it might be a different story, but then I'd probably go with a nice revolver anyway.