I have had quite a few Nikon fit 85mm's
Nikon 85mm f/1.8D - Reasonably sharp, bokeh isn't amazing, old screw driven a.f is annoying.
Nikon 85MM f/1.8G - Sharper than the old version, very sharp in fact or my copies where anyway, does suffer quite bad from C.A, very cold analytical lens with little to no character.
Sigma 85mm f/1.4 - Beautiful lens, wonderful bokeh, hard to find a good copy though in terms of a.f accuracy, a little soft in the corners not that it really matters they are wonderfully sharp in the centre.
Nikon 85MM F/1.4D - Much softer than the others wide open, but a lens with a lot of character.
Nikon 85mm f/1.4G - Have had 2 copies of these, first one was never happy with no amount of adjustment could make it perfect in terms of a.f, managed to eventually return for a replacement and it is superb in every way, lots of character, very sharp, stunning bokeh far and away my most used lens.
They are all good though in there own way, so you can't go wrong really.
In terms of value for money the Sigma beats everything else hands down if you get a good copy.