The answer to this question depends on the specific needs of the building and the environment. Air Handling Units (AHUs) are typically used in larger buildings, such as office buildings, schools, and hospitals, as they are able to provide a higher level of air conditioning and ventilation. AHUs are also more energy efficient than Fan Coil Units (FCUs), as they are able to provide a more consistent temperature throughout the building. FCUs, on the other hand, are typically used in smaller buildings, such as apartments and single-family homes, as they are more cost-effective and easier to install. FCUs are also more energy efficient than AHUs in smaller spaces, as they are able to provide a more localized temperature control. Ultimately, the best option for a given building will depend on the size of the building, the climate, and the budget.