I've experienced London and Paris but I would still swap one of them with a city in a less developed country for variety.
Say Dakar for example (2.5M people): no road signs, pedestrians on the highway, constant honking from every directions, more varied "vehicles" like horse carriage and "car rapides" (small buses).
Say Dakar for example (2.5M people): no road signs, pedestrians on the highway, constant honking from every directions, more varied "vehicles" like horse carriage and "car rapides" (small buses).