No matter where you start, it won't stop there. So just dive on in anywhere and get your feet wet! 😀
Let's say you get an M6 because its the *cheaper* option. Once you've shot with that for a while, you're gonna want to *upgrade* and try Mechanical Perfection (i.e. the MP). The best, most modern, mechanical Leica ever. Precision machined gears working in unison to advance your film and time your shutter. The pinnacle of mechanical cameras from Solms. So you sell the M6 and get an MP.
It's bliss. But after a while, you get curious about all the fuss people make regarding those original meterless Leicas (M3 and M2). The owners swear by them. So smooth to shoot, Built like tanks. They don't make 'em like that anymore. Made during the true golden era of Leica. The spell is cast upon you. There's nothing to do but succumb, so you sell the MP and get an M3.
And its pure, classical, Leica bliss .... for a while. Then, you slowly realize you're missing shots because manually adjusting shutter speeds on the fly just doesn't cut it anymore. Too slow. The action is over before you know it. So in steps the M7 with its AE mode to replace the M3. Because you *need* to shoot faster, and the M7 will select the shutter speed for you 😉
So you sell the M3 and buy an M7. Then all is well with the world. You're getting those shots that you were missing before. But the film and developing costs start to add up. And scanning becomes a chore. You think to yourself, this is ridiculous, I should go digital ...
So you unceremoniously dump the M7 and get an M9. And its bliss again .... for a while. But somehow, a digital M is not the same. The thumbs up is comfortable enough, but you miss the smooooth film advance action and manual film rewind. And the anticipation while waiting for your film to be developed. Somehow, a digital M just doesn't have the same soul as a film M. Something is .... lacking. So, you decide to throw in the digital towel, and go back to your film roots. The M9 gets sold and replaced with a ....? An M6 maybe. They're reasonably priced. Work like other film M's. Why spend the bucks on the fancier models (back to step one).