For me, 50 is nearly always the first choice, for street, portraits, landscapes, abstracts, whatever. Every other focal length apart from 40/42mm feels like trying to fit a composition to match the FL of the lens I'm using, but with a 50 I nearly always get exactly the composition I saw before I lifted the camera to my eye.
I like 28mm on occasion too, but it could never be my standard lens.
Nowadays my lens collection is limited entirely to one 28 and a couple of 50s. Don't feel the need to add to it.
Ian