Man, your dragons are really good! And these are, in my opinion, your best. By the way, my favorite is the white one. It'd be pretty interesting if you'd associate each of them an element... Anyway, good job and keep the good bits comin'!
I find the green one also pretty pleasing, but the color is ever so slightly too... uniform. Heavy. Red is attractive just because he's unnaturally bright, black is rather generic and the rest don't look fitting. The white one is the most striking. Especially the wings.