The best 35mm camera ever made? It must have been the Canon Sure Shot. Back in the 1980's at Venture, we probably sold more of them then all our other 35mm cameras combined.
A few of the customers would ask me what I shot. When I replied Contax, they had never heard of the brand! :D
best, best, best, usually means the wrong thing ... generally "highest performing". The Consumer Reports version of "best", which gets check marks in more categories, but has little or nothing to do with actual use and life experience.
I knew a man who was arguably the 'best' mountain climber of his generation. He bristled at the word "best".
"The best climber in the world is the one having the most fun!" -Alex Lowe
By this more thoughtful definition, the best 35 mm camera might be the one used the most by the most people with the least trouble and the most satisfaction. I don't know what that would be (I like mechanical cameras) but these days it might actually be a DSLR.
I love cameras. When I as young the best I could afford was a used FE. I began trading in cameras as I had a knack for repairing them (I learned jewelry and watch repair at my part-time job when I was in university). Trading in cameras allows me to finance my hobby, the list I posted shows the cameras I have now, but last year the list was different. Next year these will be gone, and I will have a new list. Each year I trade up a level, and get cameras which are more special. I have a couple literal "one-of-a-kinds" which I have taken a lot of time to restore.
I have shot with pretty much anything which holds film, and I enjoy them all. Today I was shooting with a Hello Kitty camera that cost me $1. In addition to the Hello Kitty camera, I was trying out a Nikkor SLR (oddball early Nikon F). "Best" is in the eye of the beholder, but as a repair person, and a collector of heavily used pro gear of all makes, I find Nikon to be the most sturdily built, and the most flexible. I also like the style of he early Nikon F and S cameras.
I thought this would get a lot of responses as everyone has their favorites. The things I like about the F5 is Color Matrix Metering, fast autofocus, the last Nikon film camera with interchangeable finders, and it is built like a tank. The only thing that I might worry about is that the electronics may go at some point. I also like that the FX lenses and my SB600 from my DSLRs (Oh did I say that) work fine on the F5. Many of the images in National Geographic were made with the F5 and Kodachrome.
In the past I've borrowed an M3, and while it's certainly a beautifully made camera, it didn't instill the must-have factor. The area in which Leica rangefinders excel, street photography, has been colonised to a large extent by d*g*t*l cameras like the Fuji X-series. I prefer medium format folding cameras for a larger negative and pocketable size. Pre-focused, they're hardly any slower that a 35mm camera, very quiet and cost a fraction of Leica prices. For 35mm the Olympus clamshell designs do most of what a Leica can and are shirt pocket sized.
Canon F1N, 1V, Leica M6, MP, R6.2, Contax RTS 3, Nikon FM3, and Pentax LX.