If you look at the ballistics tables in the back of the Guns & Ammo handgun annual, these three rounds overlap a lot in muzzle energy based on which brand of ammo you use.
If you go by Marshall and Sanow, the best .357 Mag and .40 S&W loads have a 96% one-shot stop rate, the .357 SIG has 92% (but since it's a newer cartidge there's less data to work from -- dunno if it matters).
The International Wound Ballistics Association wants money for a complete table of their test results, so no help there because I'm not willing to pay for it. They do call the .357 SIG "a solution in search of a problem", and suggest a .40 S&W is a better choice.