Ciel's out for revenge; he's out for blood. I'd agree with a previous poster and say that he is an anti-hero. His motives are not good, and neither is his goal, so I can hardly call him good.
Typically, when you have characters that make some sort of "Deal with the Devil", they do it for an evil cause. Ciel makes a contract with a demon in order to get revenge sooner. His "justification" doesn't matter in the slightest.