I have/used a Leica 11f , with a 50 mm collapsible F 3.5 50 Elmar since '82. I've extensively used a Leica M4 and a 35, 50 and 90mm lenses extensively.
I've got a G12.
Also Pentax slr/dslr (s), Mamiya medium format system, Zeiss Ikon, etc.
The Leica's are extremely well built. The G12, well built for a small advance compact camera. I don't call the G 12 a point and shoot...it's an advanced compact.
Pix quality...G 12 very good....Leica...excellent.
Cost...G 12, not cheap...Leica...can be out of this world.
You can't compare a G12 with a Leica Rangefinder. Different as apples and oranges.
Although having said that, I bought my G12 as a daily carry around to replace my Leica RF 35 mm in that task. I wanted to go digital.
Back in the '80's, I did some non scientific comparisons between a Leica M4 and a Pentax slr, an ES 11...same subject, same time blew up to 8 X 10's.
I used Pentax Takumar lenses. In my view i thought at 8 X 10 it was a toss up between the two makes. Zap it up to larger size prints...well I don't know. Probably the Leica.
I think there are exceptional cameras out there on the market that I would eventually like to own.
In no particular order:
Canon 5D Mk 11- a great camera, full sensor, video..capable, capable, capable.
Pentax K5...some (I do) think this might be the best cropped sensor DSLR out there currently and it is built like a tank.
Leica M9. As a long time Leica owner....I do love the unapproachable quality...the Rolex of cameras. I have used an M9....I want one.