Most powerful in ME

[The Saucepan Man]

1. Sauron
2. Gandalf the White.

Actually, my earlier question to Legolas notwithstanding, I have since been convinced (by reference to extracts from Tolkien's Letters) that Gandalf would, in his full Maiar form at least, been a match for Sauron. I do not have the reference to hand, but it refers to Olorin and Sauron being co-equal in their origins.

At the time of the War of the Ring, Sauron had diffused much of his power into the Ring. So, quite possibly, Gandalf was his superior, although Gandalf was injuncted from using his full powers. Sauron with the Ring, though, would probably have been too much for Gandalf, even as Gandalf the White.