Most of the photo real heads that I have seen lately have bean poly or subD's.

My vote is for poly, when you place your quads how a good nurbs patch model would be it deforms just the same. Now days there is more of a expectation to go farther with the face expressions. Nurbs start to look limiting in there strict adherence to how they have to be patched together.

after a point the geo is mutt. It's a great thing to have a realistic face as fare as proportions.. but its only half the story.
Textures and shaders are what is the really tricky part nowadays..

I would keep going like you are. and pour some energies in to getting a skin like shader going.

It looks like your getting a start on the shaders also.. your using something like a velvet shader on it.. to fake a little of the subsurface scattering that happens in human skin. Cool start.