Ranked by frequency of use it's: 1. 50mm/1.7 -- all-purpose, light and fast 2. 16mm/2.8 fisheye -- *really* wide (think a cathedral top to bottom from across the street). besides, i do like the distortion 3. 24mm/2.8 -- just wide and very rectangular 4. 135mm/3.5 -- portraits and whenever i want to compress perspective. This is my walkaround kit, together with Bogen table tripod. The rest (35mm, 85mm, 105 macro and 200mm) is used very infrequently.
best, Mishka