The 25-year-old has become a key player for England in recent years, setting records for the fastest ever Test 250, the highest ever Test score for a number six and the fastest ever double-century for an Englishman.
"He's a proper batsman. He's got the power but he's also got the finesse," Flintoff, who was a key all-rounder for England for more than a decade, told the Evening Standard. "He could be England's best ever all-rounder, not just better than me. Better than all of them.
"[Stokes] can perform on anything, he scored that double hundred in South Africa. He performed against the Aussies, and we're going to see him getting better and better. His bowling will keep improving — I think he'll always be a batsman who bowls rather than the other way round — but when he's got the ball in his hands, something happens.
"There's going to be a lot of pressure on him because everyone will look to Ben to turn games and he will fail from time to time. He'll fail quite a bit, but you've just got to go with that because what he will give you at times, he will genuinely win a match nearly on his own."
Stokes is currently with the England squad on a five-Test tour of India.