If you've got enough space to muffle the noise of an evaporation-type humidifier, that's highly preferable to the ultrasonic type. You might consider a steam vaporizer, possibly coupled with a small fan to disperse the steam and prevent it from condensing. If you must go with ultrasonic, you will definitely want to spend the extra money on distilled water to fill it. Otherwise, you'll find the suspended solids precipitating in corners of your closets you never thought air even reached.