i use perspective coz orthographic is an unrealistic view. with your eyes u look/see always perspective. when rendering in a big 3d app, its mostly perspective. the common setting is 60.
orthographic is only good for technical stuff that means character too (anatomy)!!! e.g when u check the size of the figure like in books (8 heads etc) because this is done in orhtographic style. or like hands are nearly as big as a head etc. perspective view would give you a wrong “value”(?)
in the past when zbrush didnt have perspective view the figures looked very strange in a 3d app with perspective.
the only downside of perspective in zbrush is that it reacts a bit strange. the default value of 60 (default=the human eye) looks a bit fishy (fish eye) i would recommend 70/80. and it reacts very strange when u just use parts of your mesh. very unrealistic!!! it seems the program takes the seeing part as a whole thing?! i hope pixologic will fix this strange behavior in the next releases.