Interesting (and sort of off track) I have never heard of the 620...I just looked it up. It's essentially an L-Frame 66. Now I need one.
Anyway, for a first revolver your best bet is a Ruger GP-100. Used S&W's are EXCELLENT values, but you would need to do a lot of research to find a good deal, and be able to assess the mechanical shape and overall condition. A new Ruger GP-100 is a quality gun with a great company standing behind it for less than what a new S&W would cost.