I'd guess 10mm will be cheaper and easier to find over there, but I could be wrong. Many new guns have come out in 10mm over the last couple of years and it has become moderately popular. .357 Sig is still very uncommon.

All of the .357 Sig ammo from Federal, Winchester and Hornady is watered down when compared to Buffalo Bore, Double Tap, and Underwood.

FWIW the .357 Sig has the same bore diameter as 9mm.