There are a lot of interesting opinions here. Of course, the original poster will have to figure out which ones actually apply to him.

My first interest in a mountain gun came when I climbed Mt. Washington and, at the top, found that I had drenched my 4" M29 in sweat. This was in September, as I recall! Fortunately, it had not rusted before I caught it, dried it off, and re-RIGGED it with grease left in the frame cutout under the grips. Not long after that, I was looking for a 629. However, the Mountain Gun that I found kicked too much. It seemed like forever before I could get off a second shot, so I shelved that idea for a while. Eventually, however, I came across a PC double-Magnaported 3" 629, which I bought, and it kicked no more than my 4" standard M29. It was also easy to conceal even on the belt (I had carried the 29 in a Summer Special). I eventually ended up with even better grips for it, and consider it a reasonable response to the situation for which one ordinarily envisions mountain guns - not too much weight in a powerful gun that can actually be fired more than once at a large animal.

I also have a 520 which can handle any .357 load, and has the obligatory standard-profile barrel, and it's certainly a fine gun, but I think that most folks who are discussing mountain guns are talking about big bores, even though they are probably not necessary except for hunting or when planning for surprise encounters with bears, which I am told are best handled with shoulder arms, which are not going to be seriously discussed by people who are concerned about the weight difference between a standard-profile barrel and a non-tapered barrel.

The last paragraph is the second-longest sentence I ever wrote.

Good luck with your search. Do try to fire the model you select before you buy it, with ammo that is what you'll use and grips that fit your hand.