Depends on the need. In the south we have ac but no one has a furnace with built in humidifier like some places up north.During real cold snaps, a humidifier is a must, to counter the dry heat, often plunging humidity to 10% which produces headaches, coughs, nose bleeds, sore throats, etc.I recommend they be on if the heat is on.Vaporizers make a mist which helps wash the airway with droplets, this can really help coughs.
Both work! Adding moisture to the air using a vaporizer or cool mist humidifier can be very helpful for respiratory infections and problems. Both work, both add moisture to the air. Warm vaporizers are usually cheaper and easier to maintain, but can pose a hazard to children if they get too close or pull on them. If you use a cool mist, make sure to clean it properly and change filters as directed.