You can probably find a 4" GP100 for less than $550. if you shop around a bit.
I own both S&W's and Rugers. Both are excellent revolvers. Rugers are built like a tank and virtually indestructable. S&W's are somewhat smoother and generally lighter. Both have their good and bad points.
If you want a good HD handgun, you'd be hard pressed to find something better than a 4" GP100. It's stout and will handle any round you feed it.
Just my 2 cents.
