Best Places to Buy High-Quality Essential Oil Diffusers Online Choosing the best place to buy a high-quality essential oil diffuser hinges on the type of diffusion you want (ultrasonic vs nebulizing), run time, desired scent strength, and long-term costs like oils or cartridges. Expert testing typically weighs design, noise, run time, tank size, and features such as timers and lights, as shown in BHG’s 24-diffuser, 2,688-hour test and Wirecutter’s long-running diffuser tests. “Ultrasonic diffuser: A device that uses high-frequency vibration...