In spite of my love for J-frame Smith and Wessons, I am tempted to suggest the Makarov due to its proximity, capacity, and utter simplicity of construction. The fact, however, that you must carry it chamber empty gives me pause and tilts the balance in favor of either Smith, whichever you feel is the better buy and you like more. I would lean toward the 640, myself.
Use It Up, Wear It Out,
Make It Do, Or Do Without