I only have two lenses so don't have a lot of choice. The kit lens is more flexible and has the advantage that it records the aperture in the EXIF data.
The 50mm lens is so manual that I have to remember where the aperture ring was so I tend to leave it in one place for a given session. Mind you, sometimes I think working within that restriction can force me to be more imaginative about the kind of pictures I take.
For example, see my recent set of pictures from the garden at
RHS Harlow Carr. That was an afternoon walking around with the 50mm (and occasionally putting the Raynox macro adapter on) and I got plenty of pictures I am very pleased with.
Of course, both are small enough and light enough that they don't pose a problem when carrying them round all afternoon; if I had some longer zoom lenses I might have a bit more to contribute!
Wulf