Well, if I may share my opinion:
The available Leica lenses I think give much more pleasing out of focus rendition than any of the Mamiya lenses do. I have used Mamiya cameras, and their lenses are sooooo sharp and exhibit amazing contrast. But, and this is a big deal for me, I just don't like how the out of focus stuff looks.
And, with a Leica rangefinder, you do have a much less bulky camera that is capable of making negatives that far exceed many people's wildest imagination. 35mm is a very capable print making medium, if you know how to apply your skill to get there. Having an enlarger that lives up to the quality of the camera is a great start!
If you don't care about the out of focus stuff, then the Mamiya 7 will probably give you better print quality. But print quality is subjective. If you want grain in your prints, 35mm is much better. If you don't want any, you still have options with films like TMax 100 or Acros, which will give you an almost grain free 16x20 print. But if you want grain free, you should probably shoot digital (to quote a good friend)...

Jokes aside, picture quality is subjective.
Here's the most important thing: You have to plan this carefully, because odds are you will make the wrong decision if you don't. I think both cameras are more than capable tools with which you can make amazing prints. But you have to examine how you're going to use the camera. Do you want to travel with 120 film? Or 35mm? What speed will you use? How do you like wide apertures? (f/4 for the 80mm is hardly making the Mamiya lens fast). Do you want to use a tripod a lot? Or hand hold? (How about an f/1.4 35mm Summicron at 1/15th of a second, compared to an f/4 80mm Sekor at 1/60th of a second? That is no less than a five (5!) stop difference with the same film, which is HUGE). Do you mind that you only get 10/12 shots with the Mamiya? Or do you like getting 36 shots per roll? Do you hate loading a Leica?
There are so many considerations that I think are almost more important than ultimate picture quality, because surely both cameras have enough of that.