For a baby, cool mist humidifiers (both evaporative and ultrasonic) are generally recommended as they add moisture to the air without introducing heat, making them safe year-round. Ultrasonic humidifiers are particularly quiet and come with additional features like variable mist control. It's crucial to prioritize ease of cleaning, noise level, and safety features when choosing a humidifier for a baby, and consulting with a pediatrician for guidance based on your baby's health needs is advisable.