Just my 2 cents worth, you won't go wrong with any of them. I have both the Redhawk and Smith 629-4. Actually it's a Super Redhawk, which I prefer to the standard Redhawk (I owned one of these too, but had to sell it for college money).
The Smith is a classic piece and has a very nice balance to it. I love the click click click it makes when you rock the hammer back. Mine has the S&W marked Hogue grips, which I really like.
My Super Redhawk also sports a set of Hogue grips, which change the entire ergonomics of the gun. I really didn't like the wood and rubber grips that come from Ruger, but the Hogues make it feel as well balanced as the Smith.
The Ruger is a beefy gal, and the cylinders are a bit longer than the Smith, which means that you have more room to load heavy boolits if you choose.
I believe all the Redhawk parts are stainless, which is great if you are going to use it in the Northwest, where it rains 24/7 all year 'round. The Smith retains a few color case hardned parts, trigger, hammer, and some internals. While beautiful, they can rust if not attended to in the wet.
It's a tough choice, I prefer shooting the Smith, but if I had to choose for down and dirty in the mud, I'd probably choose the Ruger.
Either way, you won't go wrong, WTH, get both.