I disagree to most of what is being said AGAINST the .357 in a snubbie. Personally, I don't own one. That's mainly a factor of already having a 642 wiht 38+p rating.
Why switch? If I didn't already own one, I'd certainly go for the little extra and get the .357. Muzzle flash difference between the two along with concussion, blast, recoil, etc. are not going to be contributing factors if you HAVE to use the gun. Modern .357 magnum loads will expand when fired out of snubbies, especially the lighter 110gr loads.
I'd preempt any criticism of the 357 on a few points. First, that if you shoot 38 through a 357 you will have troubles with the chambers down the road. True of competition guns, but of a gun that will likely have no more than 100 rounds through each chamber in the life of the gun it will be no problem.
Second, the .357 is uncontrollable in such a short, light gun. Again, I have to disagree. We're talking about an adrenalile-pumping life-or-death situation. Many dozens of factors are going to be more important.
I'd like to end this post by agreeing with ARUB that resale value is the key. No matter what we students of the gun say about expansion, flash, etc., the average consumer cares that he's buying a 357. If you EVER go to sell it, you'll have a much tougher time unless it is .357. Case-in-point, how much are .38 Ruger SP-101's going for now that they have the nearly IDENTICAL model in .357?
My advice is to buy the .357, shoot 357's and 38's out of it at the first shooting session and stick with what you like. In the end if you decide ever to sell it, that .357 will be worth more in resale value than it was in purchase price.