Buffalo and San Francisco are about 2,294 miles apart by road. Split the difference and you arrive near Denver, the city closest to the halfway point between them. That puts roughly 28 hr 40 min of driving on the Buffalo side and 19 hr 52 min on the San Francisco 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. Denver still makes a fair, central place for Buffalo and San Francisco to converge, splitting the travel instead of asking one side to cross the country.
If Denver doesn't have what you're after, Omaha and Kansas City are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Buffalo and San Francisco.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.