Between the .357 Sig & .40 there's no question - go with the .40. The .357 Sig is a fairly new and not very common or popular caliber. You friends could easily find themselves 10 years from now in a gun store, looking for that doggone .357 ammo, either not finding it, or only having 1 option to choose from. The .40 is a more well-established caliber, and lots of people and police departments use it. You shouldn't have to worry 10 years from now about finding a good selection of ammo. Not to mention, the .40 offers a wider variety of bullet weights and has proven stopping power.