It is a matter of personal choice of the buyers. A residential complex could offer more amenities, larger no of families to socialize, a set no of agencies to ensure daily housekeeping on a timely basis and even better security sometimes. On the other hand, a stand alone building has fewer members, hence decisions related to the society can be made faster, amenities are used by far fewer people and stress on the infrastructure is lower. Standalone buildings can be at prominent locations in the city as compared to large residential complexes that would normally be located at a distance.