The 24/2.8 was my "normal" lens for years - I absolutely love everything about it. (The 24/1.4 is even better, if you can find one that's affordable!)
The 20 and 17 are OK if you need an angle that wide. I've found the 17 to be a little vignette-y plus there's that awfully dim max aperture (4 ?!)
The 14 is spectacular, though you have to work pretty hard to find something to shoot that isn't made grotesque by its effects. "rectlinear" sounds so much better than "barrel distortion" but in fact the things it does to subject matter at the edges are just weird... whereas I find the barrel distortion of the wider-view 15 lens easier to make look natural.
The 15 and 8 take really nice pictures, if you can find subjects that work with them.