how does the .357 sig compare to the .40 or .45 in terms of stopping power? for a personal defence hangun, which caliber will do the job better.

They're all pretty close with the top-rated loads (Cor-bon, Gold Dots, etc.).

The one you can shoot best will serve you best.

Agreed. The 357 SIG is little more than a hotrodded 9mm. The very small increase in "stopping power" it provides over the +P or +P+ 9x19 is offset, in my opinion, by the increased muzzle blast and recoil. It most emphatically is not an autoloading .357 Magnum as its manufacturer would like us to believe.

For the typical non-law enforcement shooter, the bottleneck case makes for time consuming reloading. A friend has a Glock in 357 SIG and shoots it quite infrequently, preferring his 9mm and .45 ACP versions that are easily reloaded in quantity. If you're a cop shooting on the taxpayer's dollar with factory ammo, it's no big deal.

I think your money would be better spent on a 9mm, .40 S&W, or .45 ACP.