Warm Mist humidifiers work well if you have soft water. They provide a bit more comfort with the warm vapor that they produce — many people prefer that sensation, especially when they are ill with a cold.
These machines can get clogged and dirty if you have hard water with minerals in it. If that is the case, use a water softener to treat the water that will be boiled and released as steam with these machines. That steam kills bacteria and spores too.
If you thrive in the air used in a sauna and do not have concerns with children touching the machine or being in the direct line of the vapors, a warm mist model is your best choice.
Warm mist machines also often have compartments in which to place medicines that can help breathing even more. They are often smaller than cool mist machines and a little quieter. They do require more frequent cleaning because the warm water is better for bacterial growth.