Want Chrome? Buy an M2/3/4. Black versions are stupid expensive, plus, in spite of what Lenny Kravitz says, they usually look like shit. An iconic M should be chrome.
Want Black? Buy an M5 or M6. Ironically, chrome versions of the M5 and M6 will run you more because they are rarer. Both the M5 and M6 black versions are black chrome, unlike the M2/3/4, which are black paint (with the exception of some later black chrome M4s), and don’t suffer from “brassing”, which is the single dumbest affectation heretofor conjured up by Leica fanatics.
Want to avoid the herd? Buy an M5. It has a meter, and it’s a better camera than the metered M6. Better ergos, better meter, cheaper, shows you’re serious about your Leicas and don’t give a damn what Leica snobs think.
Want one iconic M body? Buy the M4. Best Leica M ever. It’s better than the M3 because it accommodates a 35mm lens without an external finder, and it’s better than an M2 because it’s easier to load and has a better film rewind. I might argue that the M5 is an even better camera, but, admittedly, the styling of the M5 is not “iconic.”
Want to be like every other dentist who’s got bitten by the Leica bug? Buy an M6.
Avoid the M4-2 and the M4-P. The original “Dentist Leicas.” Leitz produced them as cost-cutting versions of the M4 after the M5 failed to sell in sufficient numbers. These days, they’re as expensive as a comparable condition M4. Buy the M4. It’s a better camera, has better fit and finish, has an ingraved top plate while the M4-2 and P have a cheesy Leica logo painted on the top plate. As if the forgoing isn’t enough, the M4-P comes with a hideous red dot affixed to its front.
Avoid the M7. It really isn’t an M. Seriously. It replaced the sublime sound and feel of the traditional M shutter with the metalic clacking of its battery driven electronic shutter. How incredibly gauche. If you really think you need Aperture Priority Automation and a pocket full of battery power (you don’t), get a Hexar RF for a fourth of the price, because the Hexar is the better camera, and frankly, you’re not a real leicaphile to begin with.
Don’t worry about cosmetics. Ironically, most beat up users function much better than “Minty” collectors grade because they’ve been used and kept in spec via use. Nothing is cooler than a Leica that shows that it’s been well-used instead of sitting on a shelf somewhere.
Forget about a CLA’d camera. Just buy one that works; get it CLA’d if and when you need it. Stop worrying if your 1/8th shutter speed sounds slightly off. Only collectors and fondlers give a shit about irrelevant things like that. Just use the damn thing and enjoy it.
Look for bright viewfinders with bright rangefinder patches.
Make sure the shutter curtains aren’t whacked.
To Summarize: If you want a non-metered M, buy an M4, chrome or black chrome as you prefer. If you want a metered M, buy a black chrome M5. If you absolutely need AE (you don’t) to use with M mount optics, don’t buy an M7; buy a Hexar RF and use the money you’ve saved to buy 400 rolls of HP5. Whatever you buy, don’t buy something that looks like its been sitting on a collector’s shelf. It’s probably not going to work as well as your basic beater that’s been used, and you’re going to overpay for the privilege of doing so. In my mind, you simply can’t get any better than a beat up, well used chrome M4. In addition to the pleasure of owning and using an iconic photographic tool, you’ll get some serious street cred from real Leicaphiles as opposed to the status conscious wannabees toting their latest digital Leica swag.