I shoot Leica M (two M 10s and an M 10 Mono) only because they fit the way I see and work. I find the M series actually much easier and faster to use than any DSLR or other mirrorless system. Especailly for the things I shoot. I do a lot of annual reports and candid work professionally. Also a lot of formal and environmental portraits. And street work personally. For me there is no better tool for this work. I have shot with all formats (film) and owned Hasselblad 500 C/Ms, Canon F-1s (still have those) Nikon F-2 and worked with Deardorff, Calumet and Horseman large format. Owned Canon DSLRs and I have worked with all kinds of digital systems over the the years and for me Leica M really fits my way of seeing and working.
There is no other system like Leica M. They make the only true rangefinder that shoots only B&W.