A said: If the champion is either A or B, then A or B is the champion.

B said: The champion is definitely not C, but A, B, D, E and F are the champions.

C said: D, E and F can't be champions, but A, B and C are considered champions.

Ding said: The champion may be one of D, E and F, and D, E and F are the champions.

If A is right, then B is right, and the contradiction is not established (only one person is right).

If Ding is right, then B is right, then the contradiction is not established (only one person is right).

Then C is correct, but he thinks A or B or C is the champion, but A thinks (A and B) is wrong.

So the winner is C.