I've tried a bunch of LTM cameras (of which the Bessa R and the IIIg are the most usable - please note that I do mean usable, and not collectable). The Bessa R is like the M6 of LTM cameras. It is very cheap now to buy, and it just works.
If you really want to get into Leica M, I have a fetish for big shutter dials. The original tiny shutter speed dial of the M3 drives me crazy with its difficulty of use. The M1, M2, M3, M4, M4-2, M4-P, and M-A to me are usable only if you stick an MR light meter on top. That gives you a big overhanging shutter speed dial, the way Leitz intended you to use it. I have an M2, M3, and M4-2, all with matching MR-4 meters for this reason.
The M6 original version, and the MP - as beautiful as it is - don't appeal to me so much because of that vestigal shutter speed dial.
M5, M6-TTL, M7 - now you're talking big shutter speed dials. Don't look at an M5 - pick one up, and you'll know why it's such a great shooting camera.
M7: This has got to be my all time favorite M. I had a 0.85X M7 with the MP finder upgrade and optical film speed reader. It was the sweetest, fastest shooting film camera I've ever had. This is coming from a person who used a motor driven Nikon F3 for 25 years. Lost job, had to sell M7 with big regrets.
Now I've been in a new job for almost 3 years, and the first big re-acquisition was to get another M7. You can get the early versions of the M7 for about the cost of an M6-TTL these days. But, you do have to take into account that only Leica can install the optical reader (free in the USA). They will also charge you for a CLA, and more to do the MP finder upgrade. All told, it will set you back over $600 to update an early M7. I went this route with a very early M7, and I'm happy.
My choices: M7, then M5, then any of the mechanical meter-less M cameras with an MR-4 meter stuck on.