raw black i'm sure will be raw black plastic. probably see some marks where they sanded out any kind of imperfections in the plastic.
the matte black will probably be a black primer applied over top of the raw plastic.
the raw plastic parts are alot easier to prep. all it takes is a little bit of scuffing, and trim up the edges if they are kind of messy looking.
a primered part if the primer is too textured will require sanding.
i would recommend you get the raw black and have them painted at a reputable shop that uses adhesion promotor.
if you were going to leave them the way they are and not paint them, i guess the best way would be the matte black. simply because the raw plastic will waterspot really bad when it gets wet, and it etches in, and looks horrible.