"That's what I said when I left the club and I still believe that today.
"It's different class what he has done since he arrived. If you look at the results we had when I was there, even if we didn't do so well in the league, he did brilliantly in the domestic cups and the Champions League, especially with the players that he had back then."
Asked to compare Benitez with his City manager Sven Goran Eriksson, Hamann added: "They are different but then everyone has their own way of doing it.
"Rafa likes to get involved more on a daily basis, while Sven watches from the background and doesn't speak as much as Rafa.
"But they both know what they are doing and their records are both great and like I say, everyone has their own style."