I'm happy with my Nikkor 50mm f1.8 and consider it a bargain. I have never used either of the Zeiss ZF 50mm lenses, but it is the 50mm f2 macro that is supposed to be the good one. I have seen and heard a lot of reports that the f1.4 has strange bokeh in some situations. I don't think Bjorn really liked it, for instance.
On the other hand, I have the ZF 35mm, and I concur with Michael R that this lens is a gem. It is big and heavy, but gives great results and I think totally outclasses the Nikkor. If you're using it on an F100, the size and weight won't be too much of an issue, as the camera should balance it nicely.
-Laura