Atlanta and Hartford are about 845 miles apart by road. Split the difference and you arrive near Richmond, the city closest to the halfway point between them. That puts roughly 9 hr 51 min of driving on the Atlanta side and 8 hr 6 min on the Hartford 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. Richmond still makes a fair, central place for Atlanta and Hartford to converge, splitting the travel instead of asking one side to cross the country.
If Richmond doesn't have what you're after, Washington and Raleigh are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Atlanta and Hartford.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.