It depends on the design and your criteria, but factors to consider include speed and blade material. Noise can be caused by blades cutting through air or rubbing against each other. For two similar fans with different air-circulating features, there's very little difference in both noise levels and airflow at the same speed. The quickest way to find a quiet fan is to choose one that has manufacturer's decibel rating for it's noise performance - you'll want a decibel reading of around 40 or less.