Favre would be a dream come true. Not necessarily for the best of the team but for me personally.
Always wondered how he'd do with an elite team. He would be kind of a risky option, sure. But he surely showed that his tactics and handlings of difficult personalities are top class. Saved Gladbach and Hertha miraculously and was not afraid to bench big characters. Would be a nice interim choice.
Don't know about permanent, though. Dortmund was already too big for him in terms of interest, media etc.
Maybe not the best, but the most interesting option for sure!