I use V3 almost exclusively.  While I like V4's facial expressions and easy morphing, V3 always looks like a person, whereas you have to have the right texture to make V4 realistic.  V3 appears to actually have bones in her face; V4's face is unnaturally smooth.  In addition, I prefer the old "one texture fits all" idea of the generation 3 figures rather than the "let's make more money by making it impossible to swap textures" philosophy.