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Its really hard to point to any one lens as the best portrait lens.
The FA*80-200/2.8; 200/2.8, can be rated 'best' to me as well, but the working distance may be a bit too far.
FA77ltd and 43ltd are 'best' if there is a lack of working distance.
Some folks take into account the price paid for the lens, which confuses the answer even more.
If I have to pick from the ones I've used, then it would be the FA*85.
AF, fast aperture, sharp, fantastic bokeh, reasonable working distance, 'cheap' too considering its 2nd hand price vs new Canikon options.
There are others, including the K135; A135/1.8; A85/1.4; M85/2; etc, but they are MF.