I'd argue aggregating urban areas gives a more accurate perspective on the actual size of that urban conglomeration, though I understand this is controversial because it disregards more traditional views of the definition of a city. This measurement is better because it is an international definition, one that can be vaguely agreed upon by the whole world, since many countries and cultures view the idea of a city as considerably different. This is the best way to internationally compare urban conglomerations, or "cities".
Often with wildly incorrect results