Over the years I've owned and used several Nikons (an F, F3, and F3HP), and even more Leica SLRs (original Leicaflex, SL, SL2 and an R7). I've also handled for extended periods of time various Nikon F2s, an Fm2N and a Leica R6 and R6.2. Any of these cameras are capable of great shots, obviously, but the camera I keep coming back to, and my favorite by a wide margin, is the Leicaflex SL. A big, bold and beautiful viewfinder, a near instantaneous shutter (like a rangefinder), and so well damped that hand held shots at shutters speeds one or two stops slower then Nikons. I also like Leitz optics better then Nikkors.
Just to clear up a few internet myths: 1. The Leicaflex SL body actually weighs less then a metered Nikon (F, F2 and F3). 2. Spare parts are available fro Leica techs (e.g., Sherry Krauter), and generally the camera is fully repairable.
All great cameras, but for me I'll go with the Leicaflex SL. In my 800 or so rolls worth of experience in using the Leicaflex SL, they generally proved reliable. I'm not sure anyone will use a film camera so much these days that it will push the limits of reliability.
Prices have come down so much on film stuff that maybe the trick is to own some of each.