The F28/2.8 is my top choice for 28mm so far. I can only find a few flaws. It has just an ordinary minimum focus distance of 0.3m, I think good enough if you're using it as a "normal", but some lenses get closer. It has an IR hot spot. It isn't super-fast but it is the sharpest I've used, so it's perfectly usable wide open. The F lenses have that terrible thin manual focus ring, assuming AF was so great you'd never need it.
It's so awesome that the flaws are forgettable. It's nearly pancake small, probably close enough to be in a DA Limited set if you don't like the 21mm. Performance is really good - I leave open the possibility that there are better 28mm lenses that I haven't used yet, it's better than the ones I have used. Focus is zippy. I have one shot with some veiling flare but it's great compared to the cheap stuff I've tried.
I got this lens attached to an MX Data - not the data back, but a special body with a watch, a flash to illuminate the watch and a small flag in the mirror box to project the watch face onto. (There was a similar LX version) I sold that to a collector.
Here's the lens with a metal screw-on hood I used. The hood takes a 58mm cap. It's about an inch deep. I just left it on the lens unless I needed to carry the camera in a coat pocket.