In my opinion, when choosing an HVAC system for your house if you do not have one already, I would consistently request going for a central air conditioning and heating. I would not recommend getting a furnace of any kind since they are pretty much ancient. If you do have an older house with a furnace, you do want to make sure and have your local HVAC company consistently do a heating and cooling tune up at least once a year right before the freezing cold winter time begin! The older the heating system, the more they need to have an HVAC related tune ups from a HVAC, then for air conditioning, I would also recommend a full on central heating and cooling system. Window air conditioning units are still popular today in some parts of the US, depending on the neighborhood or state you live in, then 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 flooring 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 yearly electric bills in the long run instead of using regular central heating.