It is better if air conditioners run for relatively long periods of time than if they are continually, switching off and on. Longer run times allow air conditioners to maintain a more constant room temperature.
Sizing is equally important for central air conditioning systems, which need to be sized by professionals. If you have a central air system in your home, set the fan to shut off at the same time as the cooling unit (compressor). In other words; don’t use the system’s central fan to provide circulation. You would be best advised to use circulating fans in individual rooms.