I used to own a 85mm f1.4. I think it might not be as good as the 85mm f1.8.... Reason being is I find the DOF at f1.4 too thin sometimes. Most of the time I shoot at f2. The f1.4 lens is heavier and more expensive. Furthermore, at f1.4, the 85mm has serious fringing issues at the OOF areas.
I think might as well get the f1.8....
I like the focal length of 85mm though. 50mm is too short....
personally I feel the most impt thing is the focal length. 85mm and 50mm and 105mm is quite different. This is impt to me mainly because of the background. Using a telelens makes the background looks more life size compared to the subject. Basically I don't like the big human small background tree effect
Next is the DOF which is set by your aperture.
Finally is rendition of the out of focus areas. The nikkor 85mm f1.4 has quite pronounced fringing which is very distracting.
Speaking from non digital expericence, 105mm is the ideal length with a slightly soft filter. But since you're on digital, chose from 85 to 105mm with the fastest f-stop you can afford. Always use prime if you can afford.
The rest is left to how artistic you are and good lighting angles.