I own S&W K-Frames, L-Frames, J-Frames, and a Ruger GP100. My Ruger is an older (1989-vintage) fixed-sight, 3" blued model with wood-insert rubber grips. It is the best revolver I have ever owned, and I will never sell it. The ergonomics are great, and I know that the ejector rod will never unscrew, and the cylinder thumbpiece will never shoot loose. I put several hundred .357 loads through it a year. Newer GP's (Hogue gripped/adjustable sights) are nice, too, and I liken their overall feel/heft to that of a S&W N-Frame.
I use a square-butt J-Frame S&W M36 as an off-duty gun. Ruger makes no equivalent gun in feel or handling (the SP101 is too fat and chunky for a 5-shooter, and I have no use for their new LCR). I also like the classic feel of K and L-Frame S&W's. For concealment, I like S&W.
If I had a revolver as an authorized on-duty weapon, loaded with .357 Magnum ammo, I'd go Ruger for durability. Were I limited to .38 Special ammo, though, I'd go with a S&W K-Frame. I have a 4" S&W 16-3, agency-marked, in .38 Special caliber, that handles beautifully. I like the trigger stop that came factory-installed. In all but frame stamping, it's really a M15 "Combat Masterpiece". In .357, though, I'd want a heavier gun.