Hartford and Miami are about 1,186 miles apart by road. Split the difference and you arrive near Raleigh, the city closest to the halfway point between them. That puts roughly 10 hr 59 min of driving on the Hartford side and 14 hr 38 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. Raleigh still makes a fair, central place for Hartford and Miami to converge, splitting the travel instead of asking one side to cross the country.
If Raleigh doesn't have what you're after, Richmond and Charlotte are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Hartford and Miami.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.