Easy answer for me. There are only two Leica M cameras that I actually really, really like a whole lot: The M3 and the M2. I would probably pick an M2 if I had a choice between the two, just because I'd prefer its wider-angle viewfinder, and its set of frame lines. This viewfinder and frame line set fits my use of a small format rangefinder a bit better than the ones on the M3.

...and when I pick the M2, it will be one with no self timer and a button rewind: the simplest and cleanest of the M2s...and my lens set will be exactly what the camera is designed for: 35, 50, 90.