Capello has also trained the likes of Alessandro Del Piero, Raul, Marco van Basten and Francesco Totti, but he feels the retired Ronaldo, who scored 62 goals in 98 outings for the Samba Boys, was the most dangerous at his peak.
"Technically the best? Absolutely, Ronaldo - and not Cristiano," Capello said via Uefa's official Twitter account when questioned about the best hitman he has worked with.
"Van Basten was very good, but I think when Ronaldo was at his fittest, he was the best."
The ex-England tactician also picked three players he considered to be football's greatest acts.
"It goes in three different eras I think. At the start, between 1970 and 1975, this player was absolutely Pele. Then it moved to Maradona. Now? Messi."