i'd personally prefer white on the mkvi. the black is nice, but mkvi looks like it has been created to be white.
in short, the white is more of a head turner than the black.
the black on the other hand is mostly a preferred colour so i'd guess there will be quite a number of black gti's running around, and in the meantime it looks dull in black.
the story is different on earlier models of the Golf as they look great in black...the only other golf that really looks nice in white is the mk1.