Could you tell us more about your preferences, what is important to you?
Do you want TTL metering? AE operation? How likely are you to be using the 75 Summilux, 90 Summicron or 50 Noctilux? How likely are you to want to use the wider lenses?
Some random-ish thoughts:
Screw mount lenses can be used on bayonet bodies, but not the other way round.
The later M6s, the M6TTL, the M7 and the MP are available with choices of viewfinder magnification.
All but the earliest M7s and all MPs have slightly better viewfinders than the M6s, but upgrades are possible.
The sensitivity of the meter improved during the lifetime of the M6 classic, and improved further with the M6TTL. The M7 and MP continued at that level of sensitivity.
The M5, CL, M6, M7 and MP all have TTL metering for continuous light. The M6TTL and M7 also have TTL flash metering. The M7 also has auto exposure. The CLE only has metering in auto exposure, it can be operated in manual, but without metering.
The M7 and CLE are battery dependent because of electronic shutter timing/operation, but the M7 has two mechanical speeds. In auto exposure the M7 shutter is continuously variable.
The M3 viewfinder is probably the best of the bunch for use with a 50 mm lens.
There's a new limited edition M2 coming out with an authentic 1950s bakelite and snakeskin body with chrome trim. Or maybe not.
'Canadian lenses have mouse droppings in them.' OR 'They are every bit as good as German-made lenses.' Pick your own opinion.
The list goes on...