I like both calibers in question but I belive the 10mm is a superior round. It seems that the .357 Sig was designed for one main purpose - to duplicate the popular and effective 125 grain@1400+fps .357 Magnum load in 9mm sized autos. The .357 Sig achieves this goal quite well. Of course, light loads of 9mm +P+ and .40 S&W can come close to that velocity as well.

However, the 10mm is a different animal. When fully loaded, the 10mm can put a heavy bullet down range with a very high velocity, even out performing the .357 Magnum. But whereas the .357 Sig does one job well, the 10mm can do several jobs. If one needs a good hunting or outdoors gun, a 10mm loaded with full power 180 or 200 grain bullets can do the job. On the other end of the spectrum, full power light bullets can be had with very high velocity too. Also, lighter 10mm loads can be had, much like shooting .38 or .44 Special out of a Magnum. I find the 10mm Hydra-Shok to be an excellant defensive load for my Glock 20.