Wonderful question! I spent some time recently interviewing religious converts on my very un-religious campus, and I think you'll find your discussions fascinating, if not particularly epistemic-rational.

Some topics I'd bring up: Second CronoDas on "why are you not a Jew/Muslim?", as well as "what evidence (especially scientific evidence) could lead you to dramatically change your belief in God, if not stop believing altogether?"

Finally: "If you stopped believing in God, what do you think would be the consequences in your present life on Earth?" Many believers I've met seem to believe out of a desire for comfort/reassurance, which makes far more sense to me than believing based on evidence.