I have never seriously used the 35mm focal length, first of all, but am quite intimate with the 50mm, my first love. It's my answer to the "only one lens: which?" question, because it's neither wide nor long (and therefore can be either to certain extents, with technique) and because I know it well. Someone on one of these websites once described it as "cinematic" and I have to agree with that, although I can't articulate why this is so. It's a good main focal length for me because, in addition to it's versatile perspective, it can be bought new cheaply which means I can have a couple of the same on a couple of bodies, plus a back up in the bag, all for the price of many other lenses, used or new. I like it because it's "boring". It doesn't reek of optical effect, which can be used mightily to the photographer's advangage, interestingly enough.
Right now, however, I am getting to know the 20mm, and it's freakin' me out!