3. Sir Arthur Conan Doyle
Come on. It would be PERFECT. Sir Arthur Conan Doyle was best known for writing several stories that we now collectively refer to as the Adventures of Sherlock Holmes (less known for his follow-up series about a gentleman named Professor Challenger, but hey, Sherlock Holmes is a tough act to follow). Just imagine a world in which the Doctor is partially the inspiration for Sherlock Holmes rather than the other way around. I tend to have a really soft spot in my heart for the Victorian historical type episodes, so I'd love to see the Doctor tooling around London (or, even better, Edinburgh, just to give the Scottish agenda some serious momentum) with Doyle, especially if they were investigating some sort of murder mystery. Doyle could come up with some really impressive observational detective work, only to have the Doctor tell him, "Nope, I think it's just aliens." I don't think is something that could happen with Moffat behind the wheel, just because his current work on Sherlock would make it all feel a little nudge nudge wink wink, but with a different showrunner? Absolutely!