With planes, airports are way off the city centre, I think that there are few airports (here in Europe) serving large cities that can be reached in less than 1 hour from the city centre, and that applies to both A and B, to this you add, unless you use a private means of transportation (car-taxi), a half an hour for the timetable of the bus or train you need to take to/from the airport, as it won't necessarily be synchronized with your flight departure/arrival.