* Religious settings and contexts: In church, religious services, or when interacting with your congregation, Reverend is almost always the appropriate and preferred title.
* Academic or professional settings (outside of religious contexts): In a university, a conference, a professional publication, or when addressing someone in a non-religious professional capacity, Dr. is the appropriate title.
* Ambiguous situations: If unsure, it's generally safer to use Reverend. Using "Dr." might seem inappropriately formal or even presumptuous in a religious context. Conversely, using "Reverend" in a strictly academic context might seem odd or even disrespectful of your academic achievement.
In short, prioritize the title that's most appropriate for the specific setting and audience.