Jaya Ballard, Task Mage takes first place. I've had that deck for what's closing in on a decade now, it was the first deck I foiled out, and it's still entertaining to me. That's pretty good for building mono-R because people argued it was the worst.
I come back to Vish Kal, Blood Arbiter and Dralnu, Lich Lord a lot, so there's probably an argument for either of those too.