Spurs will travel to the champions, where they will face the Argentina international who has scored six goals in nine appearances this season.
The Tottenham manager told reporters: "When he plays it's like classical music, he's unbelievable, the best striker in the world. I think seriously, like Mozart. Mozart is positive and Beethoven is a little more crazy.
"For me he is the best. [Lionel] Messi is not a striker, [Cristiano] Ronaldo is not a striker, Aguero is a classical striker, he has everything a striker should have.
"I'm not biased, it's just because he's the best. But we need to make the game difficult to avoid him having the possibility to score against us."
Spurs lost 6-0 when they played at the Etihad Stadium last season.