In my opinion, when choosing an HVAC system for your home if you do not have one already, I would always suggest going for a central air conditioning and heating system. I would not recommend getting a furnace of any kind since they are pretty much outdated. If you do have an older home with a furnace, you do want to make sure and have your local heating and cooling company always do a gas or oil furnace tune up at least once a year right before the freezing cold winter months begin. The older the gas or oil furnace, the more they need to have an HVAC related tune up from a heating and cooling specialist. For air conditioning, I would also suggest a full on central heating and cooling system. Window air conditioning units are still popular today in some parts of the united states of america, depending on the city or state you live in. However, more and more people, even with older homes are upgrading to central air conditioning along with the central heating. The cost is pretty much the same to run both, so why not go for the best if you can afford to do so? And speaking of cost to run heating systems, if you have a lot of money to invest, you may want to look into radiant heated floors for your home. If you do not know about radiant heated floors, look them up online. The whole concept of radiant heated floors in itself will save you hundreds of dollars on your monthly electric bills in the long run instead of using regular central heating.