My take: Nikkor 105/2.5 (I confirm Bjørn's theory), 50/1.2, 28/2, 20/3.5 UD despite its weaknesses. Also 180/2.8 AIS, despite weight and size. 50/1.4: not initially my favorite, but I am changing opinion.
Zeiss: 35/2, esp. For Night photography
Voigtlander: 40/2, also 58/1.4
500/8 reflex more usable with Df than with any other camera.
35/1.4 AIS also quite interesting but more difficult to find; I could only shoot some test pics.
Noct seems overpriced; I had several opportunities to buy one but never made the jump.
the PC 28/3.5 is a bit expensive, esp. Considering its average performance, but it is well built, fun to use and a good teacher in slow photography. The PC 35/2.8 is usually cheaper and optically better, but less 'creative'. If you like that FL, go for it.