I am absolutely a fan of the 35mm focal length. I quite enjoy the 35mm f/1.4L on my EOS system, but boy do I love the Hexanon 35mm f/2 permanently affixed to my Hexar AF.
I just got a Nikon F3 which came with the Nikkor-H 50mm f/2. Seems like a nice little lens (going through my first roll now) I did notice a little nick in the front element, but upon close inspection I'm wondering if it is a speck of fungus.. Anyways, I like how small and sturdy it is.
If I had to choose between 35mm and 50mm, I'd probably go for the 35mm lens. When I've owned both I've used the 35mm a lot more. But, I'm actually quite fond of the compromise focal length of about 45mm. My Yashica Lynx has a nice 45mm lens, and I also loved the almost-wide angle of view of the old Nikkor 43-86mm zoom (first lens I used beyond simple cameras). This is splitting hairs, of course... if I had the opportunity to buy a Voigtlander R-series rangefinder, I'd probably get the 40mm lens.
Funny how so many folks pan the 50, yet so many of us who shoot medium format love our TLRs and folders with fixed 80s. The aspect ratio is different but the viewing angle does look really close to me. (I'm in that camp, in a way - I don't dislike 50s but picked 35 as all around more useful. But I love my TLR with its fixed 80mm. Go figure.)
In medium format, while I love the overall operation of my Rolleiflex 2.8E, in many ways, the reason I'd use it (travel) would make me want a Rolleiwide instead with the 55mm lens. Which is actually closer to a 28 than a 35. But maybe I should just take a trip with the Rollei and see what comes of it. But as a general principle, the larger the format, the less telephoto and more wide I want to be. But I've never really been a big telephoto kind of guy - the longest focal length I have in 35mm is a 135, and the longest I ever had was 200mm in a zoom. Given the interchangeability of large format lenses, the telephoto thing kinda goes out the window, but right now the longest I've got for any LF/ULF is a 25" (630mm) which would be also about a 135mm equivalent for 6.5x8.5 or 8x10.