Cech is regarded as one of the best between the posts, but the 30-year-old admits that the duo are better.
"They have kept a consistent level of performance for more than 10 years at the top for club and country," the Czech Republic told Uefa.com. "That's why they are still among the best keepers in the world."
"Each of them had something inspiring because they were all different characters," he said.
"Then Gianluigi Buffon appeared and changed everything. Later, Iker Casillas was very interesting. He started to play for Real Madrid, historically one of the best teams in the world, at the age of 17 or 18.
"So I told myself: 'OK, if he can play for a big club so young, age is not an obstacle. There is no reason why I cannot make it too.'"
Cech joined Chelsea from Rennes in 2004.