From my own experience buying and selling and using Leica gear, I like the simplicity of the M3. It's also proved for me to be incredibly reliable. Downsides, as others have pointed out, are the limited rangefinder lines. If you like to shoot wider lenses and don't like to have an external viewfinder, the M3 may not be a good solution. Also, I like using a winder. So, I liked the M4 over the M3 for that reason. All in all, if I was buying today, I would get a user M6. There seem to be quite a few available used and they don't have the collector price inflation that even worn M3 bodies seem to carry.