[jyl]

The S&W 637 is a snubnose revolver - light, compact, lesser cartridge, only 5 rounds, hard to shoot well, unpleasant to shoot for long, but very easy to carry. I have one.

The Ruger SP101 is a larger (full size) revolver - heavier, hard to conceal (but great in the nightstand), Magnum, 6 rounds. I don't have one, but it should be easier to shoot well and pleasant to shoot, especially if you do most of your practicing with .38 Special.

You can fire both 357 Magnum and 38 Special in the Ruger. You cannot fire 357 Magnum in the S&W, or you can but will damage the gun.

Unless you plan to carry it on your person, I'd get the Ruger. Rugers are quality guns.