Sauron Greater than Morgoth...

[Inziladun]

Originally Posted by Eäralda Halatiriva

it is said often that Gorthaur was the mightiest of the lesser Valar. such a statement is given to us about Melkor, as well, in comparison with Manwë. is then Gorthaur the mightiest, or would Ëonwë, who like Manwë in comparison to Melkor has greater authority or formal power, surpass Gorthaur?

I don't recall a reference to Sauron being "the mightiest of the lesser Valar", though it is said in The Silmarillion that

Among those of [Melkor's] servants that have names the greatest was that spirit whom the Eldar called Sauron, or Gorthaur the cruel.

Valaquenta

That just indicates Sauron was the most powerful of Melkor's minions. His relative status among all Maia would seem to be a question mark.

As for Eönwë. it was said if him that his "might in arms is surpassed by none in Adra". So in hand-to-hand combat, he might have an edge. Otherwise, though?
As the herald of Manwë, certainly Eönwë would have greater authority, but as for his "ranking" in raw power in comparison with the other Maia, I would say we can't know for sure.