Ferris made a big impression for Britain and Ireland's elite in South Africa but was forced home early with a knee injury.
The big blindside played just twice before injury struck in 2009, although he scored a try in each game against the Golden Lions and the Cheetahs.
He has since gone on to fully establish himself in the Ireland starting side and is currently a favourite to earn a second Lions call up in 2013.
And by time the Lions head to Australia in less than 16 months, Best believes Ferris could well be the globe's greatest.
"It helps that he's a bit of a freak of nature with his size and speed but he puts in a lot of hard work," Ferris told the BBC.
"He tries to portray this carefree 'I do what I do' attitude but he works very hard on his game.
"You just have to look at the way he's improved as a rugby player over the past two or three years. It's not just brute force and ignorance any more with him - he's turned into a very, very good rugby player.
"He's got an ambition to be the best player in the world. And the way he's going at the minute, at 26 years of age, you'd have to think that it probably isn't going to be long before he's not just talked about in that way but he actually is the best player in the world."