I own three Smiths, two Rugers, two Taurus's and two Colts. I do not own a GP100, nor have I ever fired one, but my experience with my own Redhawk and other peoples' Super Redhawks tells me that the Ruger is every bit as capable of refinement as a Smith. That said, unless you want to shoot really heavy loads, the Smith should hold up just as well as the Ruger. It comes down to aesthetics, ergonomics and (the most important -ics) economics. If budget isn't a big deal, try to find a Smith stocking dealer special with 5" half-lug barrel and fiber optic front sight. It is the epitome of the "modern" revolver, complete with Ahrends grips and an extra hole in the cylinder.
When it comes to bigger bore guns, Ruger is the only way to go. I have a smith 25-5 in .45 Colt, but that is a purely target gun. For serious work, either my Redhawk or Bisley Hunter in .45 Colt are the way to go. That is a situation in which Ruger's strength really does make it an entirely different class of gun.