P239
I have a P239 in .40 S&W and I love it! I've never shot the .357 sig round, but I've considered buying the .357 barrel, it only costs about $100. That would be my suggestion, buy it in the .40 S&W, and then buy the 357 barrel. Then you got the best of both worlds.
One more reason to buy the gun with the .40 barrel, then the .357 separatly is that the .357 Sig round will fit in the .40 S&W Magazine, but the .40 S&W round will not work in the .357 Sig Magazine.
I hope I was helpful.