Unless you want to stick with window units, you really have two choices when it comes to cooling your home: ductless mini-split AC systems or central AC systems. Ductless systems consist of an outdoor compressor and air handling units that blow the cool air through your walls. Central AC systems have an outdoor compressor, indoor coils, and ducts that deliver the cool air through vents in your floors, walls, or ceilings. To figure out which is the better choice for you, ask yourself these questions.
Do you already have a central, forced-air heating system?
If your home has forced-air heating, then adding central air will certainly be the easiest option. Your HVAC contractor can integrate an air conditioner with your existing system. The same ducts that deliver your heat in the winter will be used to deliver your cooled air in the summer.
If you do not have a forced-air heating system, then adding central air will be a larger project. Ducts will have to be run through your walls. This may not be a major issue if you're already doing some remodeling, but it can be a rather extensive and expensive undertaking otherwise. A ductless AC system is often the better choice in this case, since the air will be carried through outdoor pipes rather than indoor ducts.
Do you want to be able to control the temperatures of various rooms or zones individually?
If there's a section of your home that you barely use and don't want to pay to cool, then a ductless, mini-split AC system may be the best choice – even if you already have forced-air heating. With a ductless system, each air handling unit has its own thermostat, so you can save energy by only cooling the areas you need cooled at any given time. With a central AC unit, you typically have one thermostat, so you'll have to pay to cool the whole house even when you're just using a couple of rooms.
How do you feel about air handling units on your walls?
Some homeowner are bothered by the presence of air handling units on their walls. The units may interfere with decorating or may be considered unattractive by some. If aesthetics are of the utmost importance to you, then it may be worthwhile to have central AC installed, even if it costs more or requires some remodeling, since you won't then have the air handling units to worry about.
To learn more about both types of AC and what having each installed would mean for your home, talk to an HVAC contractor in your area.