Northeast Coast to GA down to FL would be interesting. It all depends if they can come up with a method of fast travel that makes sense in a post-apoc setting. Maybe someone still has one line of amtrack running? The GA setting could carry over some themes from the recent Walking Dead series. ATL CDC, etc... FL has swamps that would make a great setting.
I really like NYC for a main setting, similar to the Escape from New York movie. Obviously a super diverse population. Plus, NYC has awesome infrastructure to mess with. Crumbled skyscrapers and bridges. A wild Central Park. The subway, sewers, and the sub-levels even below the subway and sewers are ready made dungeons. Underwater tunnels to cross all the rivers. Stadiums to turn into castle-like fortresses. The 5 Burroughs for gang war. Maybe secret bunkers and vaults under banks and municipal buildings. Plus all the great landmarks of NYC to lovingly destroy or change to suit the purposes of the game designers.
Plus you have the Central Park mounted Rangers, and the Rangers NHL team. What more can you ask for as story starting points!?
Or maybe it's cause I live there and everyone would naturally be partial to their home regions...