Some have been surprised this year as Vettel, despite his domination of the sport for years, has struggled to keep up with his new Red Bull teammate Daniel Ricciardo.
But Spaniard Alonso on Wednesday said it has been no surprise to him.
“In my opinion,” he is quoted by Italy’s La Stampa, “Lewis Hamilton is the best driver.
“I don’t know what problems Vettel is having this year, but I have not changed my mind about him — he is not the best.
“It is others who have to change their opinion,” Alonso added.