Comparing the two cities overall, Santo Domingo is unrivaled and unmatched in shopping/dining/accessible amenities, it's like comparing Miami to Fort Lauderdale. As others have mentioned, the Capital has the Zona Colonial--a major gem the city has that no other place on the island does. Yes, there is alot of traffic, just as would be expected for the largest city in the Caribbean and not much different than other major cities in the LatAm region with large populations. The supposed low traffic and cleanliness of Santiago is a myth and greatly exaggerated as once you step out of the more affluent areas one immediately sees cleanliness is not really athat consistent. With Abel Martinez no longer, or soon to not be any longer at the helm, it remains to be seen if what he started will be maintained. If there's any place that can "brag" about cleanliness that would be Bani--no other town or city on the island rivals them on this. SDQ may not have mountains, but there is easy access to such scenery via places like San Jose de Ocoa, San Juan de la Maguana, etc. There is ridiculoulsy easy access to beaches, not just Boca Chica (which you can either love it/hate it) but there's quick/easy access to beaches such as Juan Dolio, Bayahibe and others along the southern coast.