Amongst the many fine 'normals' 50 or thereabouts, my preference on the Df is for either the 50/1.2 or the latest 50/1.4 AIS. That is, if you haven't the lust or means for the Noct of course. The f/1.2 is quite temperamental, but rewarding in itself to tame, and the f/1.4 is a very fine all-rounder.
I briefly tried the old 58/1.4 and didn't like it enough to buy it. Your mileage may vary, though. These old lenses have a charm of their own.