For SLR, I started with 50mm, having used 'normal' lenses for a lot of photos prior to getting an SLR. When I started to photograph more, I just 'knew' I needed more lenses. I ran across a kit of 28mm and 135mm. I was happy. Partially from my shooting experiences, and more from reading the many fine photo magazines, it didn't take long to realize I needed more. I thought I liked long lenses, but first was able to get wider lenses for those many shots I wanted in tight spaces. I have tried and have had, primes from 18mm, 24mm, 28mm, 35mm, 50mm, 135mm, 200mm, 300mm, and 600mm cat. They all had their uses. Of course I wanted zooms so I got 5 or 6 of those too.
I have come to prefer primes. I try to take what I think I am most likely to use, with a preference for wide as I seem to see wide. But I do have a kit consisting of a 50mm f/1.4, and zooms from 18-28, 28-70, and 75-150.
All to say I don't have just two or three favorites I always carry with me.