The short answer is that a fast mid range prime is better than a less fast zoom because of ability to use differential focus moe dramatically. Bokeh will vary according to lens - check out reviews on photozone.de. However, if you don't need totally oof backgrounds you are likely to find the zoom more generally useful. Personally, I very rarely use my 85/1.4 but if I was a portrait photographer I'm sure it would live on my a900.
Re 85/1.4 vs 135/1.8, the latter, which I have not used, is said to be bitingly sharp, which would be fine for character male portraits but possibly unflattering for females. As to which is generally more useful on ff, the 135 would give a tighter crop and also flatten features more than the 85. Personally, I would say that the latter would give a more natural perspective and you can always crop in post processing if you wish.
If you are using an APS-C camera and want a fast prime consider the 50/1.4 - the 75mm equivalence is a good portrait focal length and the DOF equivalent of about 2.1 is fine for decent differential focus.
As far as FF is concerned there is also the a900 to consider - there will no doubt be a few around.