New York and San Diego are about 2,428 miles apart by road. Split the difference and you arrive near Oklahoma City, the city closest to the halfway point between them. That puts roughly 27 hr 46 min of driving on the New York side and 23 hr 52 min on the San Diego 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. Oklahoma City still makes a fair, central place for New York and San Diego to converge, splitting the travel instead of asking one side to cross the country.
If Oklahoma City doesn't have what you're after, Kansas City and Dallas are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between New York and San Diego.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.