I used to have this dilemma as well. Then I bought all three 35mm 1.8, 50mm 1.4, and a 85mm 1.8.

I found out that I used the 50mm most, followed by the 85mm on my DX (Nikon D80) camera. Almost never touched the 35mm.

Recently I bought a 2nd hand full frame D700 (awesome camera!). Then I found myself using mostly the 85mm