It really depends on the size of gun you are looking at. If it's a lightweight snub, then most people are going to tell you that a .357 is unnecessary, and will kick too hard in your hand. If it's a bigger gun like a GP100, then .357 is a good option to have.
Oddly enough, I just picked up some .357 CCI Blazers at a local shop for $4 less a box than the same brand and weight of .38 +p ($21 vs. $25 a box). I don't know if that's just a result of the current price fluctuations or what.