B&W by far - mainly because the image becomes less "literal" and more "graphic" instead.
In the color shot, her mouth pose really stands out: it's unnatural and too tentative...caught in between the snarl it should have been, and the uncertain state it came from.
Her make-up becomes more dramatic, which the image really requires to pull it off.
In my personal view though, even the B&W version cannot fully escape the "confusion" in the composition. Why the heck is she opening her mouth like this? Given her tentative look, the idea that she is about to bite the necklace doesn't come across clearly. Or is she supposed to be in awe somehow? Or is the mouth supposed to convey some form of ferocity aimed at the viewer? Her eyes would suggest so. Her eyes should be at what she is about to bite, if that's what is going on. Otherwise it's somehow a derivative of how pornography is usually posing female models. All in all, the B&W version handles all this better, I think.