City have not found their form of last season and rival teams have made new signings but Roberto Mancini's men are still top of the table and Aguero feels that speaks volumes.
"I'm sure we will retain our title," said the 24-year-old forward.
"It's true Chelsea, United, Arsenal and other teams have strengthened their squads intelligently compared with last year.
"But we're the champions and they want to take us on, so it's to be expected.
"It won't be easy for them as we're growing as a team and we get to know each other better each time we play. We're destined to win more trophies and barring any major setbacks we will. "When I first arrived at City after my first game against Swansea, I said I hoped that this was the start of something big.
"Our Premier League title showed it possibly was and that we had great things ahead. As I said, I firmly believe the best is yet to come.
"It's true we don't have the same flair in games we had last season and we've scored less goals for sure.
"But the Premier League table says something different. We're hard to beat, top of the table and defending well so we can't be doing that badly can we?"