Columbus and Miami are about 994 miles apart by road. Split the difference and you arrive near Charlotte, the city closest to the halfway point between them. That puts roughly 7 hr 17 min of driving on the Columbus side and 13 hr 44 min on the Miami side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Charlotte still makes a fair, central place for Columbus and Miami to converge, splitting the travel instead of asking one side to cross the country.
If Charlotte doesn't have what you're after, Atlanta and Raleigh are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Columbus and Miami.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.