If I had to choose from r1k's options, I'd have to go with either the middle two, or the one on the bottom left, which look the most "menacing", partly because of their value work, I suppose. I do appreciate the metallic effect on the upper right one, but yellow is probably too bright of a color, especially on a dark background (I'm assuming this is for that space shooter you were working on?).
Perhaps you could make dark spots a bit larger as well.