The 28mm f2.8 is very sharp, I have two of them. The 28mm f2 is said to be very good too, and offers the f2 aperture, but it is expensive. The f2.8 can be had for less than $100 in nice condition. There is also a 28mm f3.5, which I have not used. It is cheap, typically $50 in nice condition. It has long had a reputation for not being as good as many other OM lenses, but lately, I have seen a lot of people online praising it. I think I'd go for the f2.8 if you don't want to pay the $350 or so the f2 lens costs. The 2.8 is fairly cheap, very sharp, and easy to find, and easy to focus.
The 50/1.4 was made in several versions because it was made the whole time the OM system was made. The best is the last version ,whose serial numbers are 1,100,000 and higher. I have two of them and one with a serial in the 600,000 range. The lower numbered one is not nearly as good wide open and has harsher bokeh.
The 50mm f2 Macro OM lens is the sharpest 50 that Olympus made. Mike Johnston from the online photographer says its one of the sharpest 50s ever made by anyone, ever. I agree. I have one, and it is incredibly sharp, even wide open, and it focuses to 1:2 without an extension tube (1:1 with a 25mm extension tube). It has better bokeh than any of the f1,4 zuiko 50s, but it costs $500 or more used.