Depends on your definition of best. The most cost and air purity effectiveness is literally just a box fan with a filter meant for an HVAC sealed around the in

Depends on your definition of best. The most cost and air purity effectiveness is literally just a box fan with a filter meant for an HVAC sealed around the intake end. If you want to be clever you could go further and make a cube of filters and control the fan with controllable power outlet or something. However if your value lower sound, form factor, or aesthetics, that make things more complex on whether a price overhead is justified. Some filters will clean the air more quickly, but a filter that needs more “passes” of air through it to clean may still reach the same level of cleanliness when given enough time. Like when you have a quiet fan always running in a room like I do.