I would get a Ruger 4" GP 100. I bought mine about a year ago and really like it. I got rid of the factory Ruger/Hogue grips and got a pair of the old style factory Ruger/Lett grips. I find the grips a lot more comfortable and stylish. They are slightly smaller though, so the gun doesn't feel as balanced (slightly nose heavy) but not really too bad.
In terms of fit and finish, I would say (comparing the current production stuff) Ruger and S&W are pretty equal. (S&W quality control has gone down and Ruger quality control has gone up.)
Currently, Ruger is selling a Wiley Clapp edition GP100 that IMHO is about the perfect configuration.
Sic Semper Tyrannis