35mm by focal length, but I do seem to shoot 35mm a lot in low light. The fastest 35mm for my Pentax cameras that I'm aware of is f/2 and it's spendy. If I could get a 35 1.4 like you Nikon folks....but then again I imagine those aren't cheap either.
I got back from South East Asian and was shooting Angkor Wat with my Canon f1N and my 35mm FD lens. I also brought my 50mm, but the perspective was too tight for me. Somehow, the perspective of a 35mm lens feels natural to me.