[Formendacil]

In Unfinished Tales, "The Quest for Erebor", Gandalf goes on for some time about what the effects on Middle-Earth would have been without the events of The Hobbit. Bearing particularly on this situation, he refers to the devastating effect on Rivendell had Smaug not been killed, and from the passage, one gains a direct feeling that although Sauron might not have had direct control over the dragon's actions, he would definitely have been able to use him, and would have been the senior partner in any partnership they might have formed.

So I agree with Thinlómien, Smaug ought to be placed below Sauron.