I have not used the older AF 85/1.8 D but from comments I have read, the background bokeh wasn't so smooth unless you get relatively close to the subject with a distant background. It also flares when shooting into light and shows purple fringing in some situations (correct me if I am wrong). It is a "screw-drive" AF lens so focusing is noisier than the AF-S version and no instant manual over-ride. I think in most respects, the AF-S version is a better option. I am sure a good used example could be found on auction sites without too much difficulty.
Of the manual 105mm micros, the 105/4 has what I would describe as "neutral" bokeh. It is not smooth like the AI 105/2.5 but it's not terrible either. With a maximum aperture of only f/4 the ability for shallow DoF effects are limited. On the other hand mechanical vignetting is very low so background blurs remain nicely rounded well out to the edges of the frame (no swirly bokeh). I have taken some good portraits with this lens.
The AIS 105/2.8 micro is also not as smooth as the 105/2.5, but I have been surprised how good it is - it is sharp and backgrounds are quite nice. The main disadvantage is the short focus throw at non-macro distances (but much better than the AF version), and the straight-edge aperture blades cause background blurs to be distinctly polygonal rather than slightly rounded as with the AI 105/2.5.