I own a retail store called Rangefinderstore.com and have used and sold all three models.
Personally I shoot with an M6 and a Zeiss Ikon... and a CL but that's not part of this issue.
The Bessa's are OK. I like the R2M better than the R3M because of the framelines. I'll never use a 40mm since I don't have one and few models exist so having those framelines doesn't help me much.
The R2M's are not an older model, they are both current. By the way the R4M most likely is the most useful model if you are using wideangle lenses.
The Zeiss Ikon is a very nice camera, the viewfinder is great and it has the useful range of framelines. Construction is good but will breakdown with real rough and heavy use. Mine has been through China, Haiti, Malawi and a bunch of other places with rough use and I did have to have it tuned up after a few years.
The M6 is a great camera but most of them are now 20 plus years old. Most of them need a tune up even if they seem to be working fine. The M6 I have is my 5th one, so I guess I really like them. Great framelines, manual shutter, nice build and you can always sell them and get your money out.
If I was buying a rangefinder I would look for a nice M6 or a new Zeiss Ikon.