Violet
He's clever. I think it's a big risk to take in the unlikely hope that he may slip up and reveal something that the Prophet didn't cover, but let me know how it goes.
Merlin, they really are pieces of work. There's probably only so much they can do. I mean, if it was a matter of driving them out, McGonagall could have likely done that all on her own by now. And Flitwick is a champion dueler.