Black. 100%. I've got Moonwalk Grey with black roof/caps and changed from silver to black wheels. They look "meaner".
The only thing that was holding me back is my parallel parking is urm, well nevermind, I was worried I would scratch them (and black alloys look worse then silver, scratched). I've put more effort into my parking in anticipation of when mine arrives.
Black. Do it.
Black is good for the perfect parker and those who think their car should rule their lives, not the other way around. But should you ever touch a kerb, black will show badly.