As a shooter of both 35mm (Leica M) and 120 (Mamiya 7) I would say without a shadow of a doubt get a M. If money is a factor I would go as far as saying forget the MP and get a clean late serial M6 and put the rest towards lenses. I think the MP is a 'sweeter' camera but for the price difference you can throw in a used 35 Summarit and possibly a 50mm planar too.
FWIW I generally print quite large and while the look is different, wait to see what Delta 100 or similar does at 20x16 from good RF lenses. Sure, the grain is there on close inspection but the detail is incredible.
The M is far quicker in use, ahs fewer film changes, has faster lenses available and is IMHO a much, much better street camera. I use the Mamiya when I know I can amble about and shoot more scenic shots where I dont need to be so quick off the mark.
A 35mm Delta 100 shot has finer grain than 120 TriX in my experience and about the same as Neopan 400. If you want untimate smooth tonality, there is no beating the larger neg, but a fixed lens? Not for me.
For my next trip to India I will be taking the Ms instead of the Mamiya kit I used last time. I realised that I enjoyed many of the images off D3200 and was often shooting (with mostly 400 film) at light levels that would allow good speeds and apertures from 100 speed film on 35mm; however, also having D3200 and 400 speed films would give me more flexibility in low light considering the ability to use wider apertures for equivalent DOF. Personal choices, but I would not want to go anywhere without either 35mm on 135 format or 65mm on 6x7.