PTAC vs. HVAC
PTAC and HVAC aren't exactly opposites. In fact, PTAC (which stands for Packaged Terminal Air Conditioning) is considered as a part of HVAC (which stands for Heating Ventilation and Air Conditioning). With PTAC systems, however, each office (or classroom, hotel room, etc.) has its own controllable air conditioning unit, which may or may not include heating as well. With these units, there is far more individual control so that comfort levels can be customized.
With central units, there is one central controller, and for various reasons, some rooms will end up more comfortable temperature-wise than others. There are climates and situations where a centralized HVAC unit is best, and there are other situations where PTAC units are the best choice.
One factor that makes a difference is climate. PTAC units aren't as efficient as centralized units, so climates that are very hot or very cold, or that have very hot summers coupled with very cold winters will save energy and money using centralized systems.
Building layout has a lot to do with the choice too. Large shopping or otherwise open spaces generally can't be heated and cooled well with PTAC units. But buildings with lots of smaller rooms, such as hotels, offices, and schools, PTAC units are better. An office located on the southern facing side of a building will have different heating and cooling needs as one located on the northern facing side of a building.
When it comes to maintenance, PTAC units will be a bit more of a chore than centralized units because there are that many more filters and units to inspect. And maintenance is important for PTAC units, because the better they are maintained, the less likely they are to break down or need new parts. While looking for visible dirt is important, there can be contamination that is invisible to the unaided eye. It is important with PTAC units that outdoor coils are free from debris. The maintenance of these units is fairly simple, but can be tedious.
With centralized units, coils and intakes need to be free from debris too, and filters must be cleaned or changed regularly.
PTAC units are more energy efficient than ever, but they still don't match the efficiency of centralized units. However, there are some situations in which the individual control of the units outweighs the possible energy savings from centralized units. This is particularly true of places like hotels, which want to give guests control over the climate in their individual room.
Generally speaking, the more extreme the climate and the larger the area to be heated or cooled, the better a centralized heating and cooling system will be. And the more moderate the climate and the smaller the individual areas to be heated or cooled, the better choice is often a PTAC unit.