Are ultrasonic (water) or waterless diffusers better?

It depends on your goal. Across the reviewers we read, ultrasonic models like the ASAKUKI and InnoGear units are cheaper, add humidity, and run for hours on a tank, but specialist communities note the scent can fade after a couple of hours and tanks need regular cleaning. Waterless cold-air diffusers (Airversa, AROMADD) use undiluted oil for a stronger, longer-lasting throw and cover larger areas, but cost more and use pricier fragrance oils. For bedrooms and casual use, ultrasonic is the budget-friendly pick; for whole-home or hotel-style scenting, waterless wins.