[Suzerain of Sheol]

Dolly, I think Rue would have the best bet in Thyati'ra. Not only does the Prelate there have a lot of information on Hell thanks to the huge library he keeps and his experience battling demons, but he's by far the most earthly of the leaders of the Churches and the most likely to be willing to negotiate. Of course... he's also the most overtly dangerous. :p