Rosberg told Austrian newspaper Kronen Zeitung: "I have giant respect for Ferrari, who were in no-man's land last year. The fact that they now lead is very, very impressive.
"But I still believe that, although it is still exciting, Mercedes will win in the end because they have the best car."
Told that Hamilton must therefore be the favourite, Rosberg responded: "Please do not forget about Valtteri Bottas.
"He really has a chance as he is fast and perhaps a bit more consistent than Lewis. Lewis is unbeatable on good days, but he also has a few more difficult weekends for various reasons."
Rosberg also said that Ferrari's Vettel could have the edge over Hamilton, due to the German's mental strength.
"We sometimes see this strength in Vettel go into unfavourable situations like Baku, simply because his self-conviction is so great.
"Lewis is a bit more inconsistent in the head, as it's important how he arrives at the race track - is he at 100% or only 95? So maybe this is a slight advantage for Sebastian."
The 2017 championship resumes on Sunday with the Belgian Grand Prix.