sculpting in zbrush is fine and dandy, but unless you start it out with good geometry in maya you'll usually end up doing as caligraphics mentioned and retopologize it later.
-don't think think that it'll be any more awesome if you aren't sure about your anatomy though.

Anyway, I usually just end up using zbrush for displacement/normal projection rather than pure modeling

I started in max, so I model with edge-extrusion because it's optimized to work quickly with that method. Usually with a polyPipe for the eyes and the mouth, then slowly connecting them up. This method allows you more precise control over the topology and smaller forms, usually at the cost of the overall form that box modeling will let you in on.