I bought a M7 new in 2003 instead of a M6 because of the features. I'm very happy with it and won't sell it in any years in time.
I also bought an old & battered, but technically perfect, Leica M4-2 (all mechanical, no electronics). I like the M4-2 better than the M4, and would prefer the M4-P even more (but was too expensive for me).
The M6 and M7 are both legendary rangefinders. Major difference: M6 is all-manual exposure, M7 has also aperture-priority.
The M6 is all mechanical (= no batteries) and the M6-TTL and the M7 need batteries.
If money is an factor, get a nice M6 and spent the rest of your money on good glass. Also a technical perfect camera with cosmetic flaws is much cheaper and easier to use without the fear for scratches .....
I also bought the Leica M motorwind (new type) for my M7. It's great and gives even a better grip to the camera.
Here are some sites that might be helpful deciding what you need/want:
http://www.cameraquest.com/mguide.htm - (Leica M buying info)
http://photo.net/leica-rangefinders-forum/00Mf55 and http://photo.net/leica-rangefinders-forum/00a3cm - (users compare M7 with M6)
BTW: the Leica SL (or SL2) with older Leica-R lenses are also very good, but a lot cheaper!!
Also build like a tank, very nice contrast in B&W and a real "clunk" when fired.