ai ai ai......what a question!
first off, welcome to RFF! and the madness that seems to go with it!
All three of thos cameras are substantially different - as you obviously know from drooling over the spec sheets and reviews.
The Mam 7 is a wonderful wonderful piece of kit, you will definately get the most detailed shots from it. The big question with a Mam 7 is - do you need that big a neg? If you're not going to blow it up to poster size then all the extra size and bulk of the gear (even tho it's a compact MF) is wasted. If you do regularly want to blow up to 20" x 30" or similar size then MF is the way to go. However another thing to consider with MF is that all the extras - enlargers scanners projectors etc etc etc - are more expensive.
If you don't need that kind of enlargement, then the choice between the M6 or the G2 comes down to the degree of automation you want or need. Either system has the ability to turn in stunning results.
But don't forget to have a look at the Voigtlander range, either. For a fraction the cost of the Leica or Contax they have some fantastic kit........ It's the old 80/20 rule - you get 80% of the product for 20 % of the price. Actually, with the Voigtlander gear, mostly it's 90%. Again, do you need the last little bit that the Leica/Contax provides? Or alternatively, are you prepared to spend the extra money just to own something so nice?
A number of us here have already made THAT particular decision.
A nice alternative in the 35mm space could be a Voigtlander body with a Leica lens - keeps costs down, gives you a faster more accurate not prone to sunburn shutter (albeit slightly noisier), slightly smaller and lighter body, and the great glass..........
Ultimately, only you can decide. But there's two specific pieces of advice I'd give:
1) Think very carefully about what you want the kit to do. And be honest with yourself about it. Don't fall into the trap of buying gear that basically isn't suitable for what you want to do.
2) Once you've worked out point 1), just buy what you really want. Because if you make a compromise you'll end up trading up to what you wanted in the first place.
Welcome to RFF!