RE: Taurus 605CHB or Smith 640?
If you plan on pocket carry, I would consider an airweight or titanium over a steel revolver. If you plan on carrying it in a holster all the time, the weight difference isn't as much of an issue.
The S&W is a better made gun than the Taurus. A Smith's double action trigger is definitly superior.
I own a S&W 340 Titanium/Scandium 357 Mag. It is my favorite warm weather carry gun. I can slip it in my pocket and barely know it's there.