I have to disagree with your sweeping statements regarding the M3 being the worst M viewfinder.
Over the years I had the chance to compare my M3 (DS) to various other M models I have or had in use, including my own M2, my own M4-2 and also an M6 and M7 that were lent to me by friends. My verdict ist that the optical quality and precision of the M3 viewfinder is unsurpassed. It is the easiest to focus and the only model that always maintains a crisp and clear rangefinder patch, no matter how adverse the lighting conditions are. It is also the only viewfinder that allows me to reliably focus f1.4 lenses wide open at close focus, while the hit rate with the smaller magnification viewfinders is more like 5/10. It also is the only viewfinder that allows me to have both eyes open while framing/shooting, which can help a great deal when composing a dynamic scene with objects moving in/out of the frame. For someone like me who uses the 50mm lens most of the time, an M3 is the logical choice. 50mm is the classical rangefinder focal length and is also the focal length with the most interesting line up of lenses. For the rare instances where I want to use a 35mm or wider lens, I can easily add an external viewfinder or with some experiene, simply guess the 35mm field. It works well enough. Of course, if you shoot a 35mm lens most of the time, I would agree that the M3 isn't the best choice. For everyone else I would recommend to look through the viewfinder of a M3 only once in their lifetime and come to their own conclusions