I picked a 442 for its easier to see sights (I shoot it a lot at the range) and for its lower visibility in case I'm concealing with a jacket which might get moved in a way to expose the gun in its IWB holster.

BUT - as others have noted, they are prone to rust. My yoke will rust if I don't wipe it down after a day's wear, and my cylinder has a spot where the finish has gone away. This occurred when I first started carrying it, and I treated it like the Glock it replaced - i.e., carry it and forget it. After a week or two I happened to check it out and was dismayed to see the rust. If I had it to do over I'd have picked a 642 and painted the sights.

In fact, I have recently acquired a 649-3 in 357 (I'll put one magnum round through it some day, just to say I did it, but in practice it's a 38 Special gun for me.) It's all stainless, with a 2 1/8 heavy barrel. I painted the sights (red ramp and black notch) and now carry it almost exclusively despite its extra weight. No rust worries, and it's a lot more pleasant to shoot +P loads through than the lightweight. If I have to carry in a jacket or pants pocket I'll take the 442, but otherwise I'll put up with the extra weight of stainless.