Oh no, I hear ya. Sort of like that... uhh... I think it was called "deadliest warrior" or something. It was really stupid, but fun. Anyway, I would vote that the Witches would win. They would more likely have better climb rates than the griffins and carry heavier armaments than your typical rider. Thus a trained Witch could out preform a skilled Griffin Rider, but it really all comes down to who's flying what. If the Griffin Rider is smart, he/she could try to use their potentially more manuvarible griffons to try to get a foolish Witch to dogfight. But the one thing any Witch worth her salt will remember a key thing from their training. To quote the most successful fighter pilot of history, Eric Hartmann, "Dogfighting? It's a waste of time." Thus, it would be hard to lure a Witch into a dogfight.
Can you tell I'm bored?