What are the best air conditioner vent filters?

If I understand your question correctly, you're looking for something for your vents and not your HVAC unit.  If this is correct, and you’re looking to control allergens in a specific room, an easy way is to use the Allergy-Free Vent Filtration Kit.  With this Vent Filtration Kit, you’ll have everything you need to filter airborne allergens from your home’s central heating and cooling system before they come into the room.  You can use the filter media provided in the Vent Filtration Kit  in your bedroom, your child's room, or anywhere in your home where you want to be free of the worry of allergic reactions. 

 

Simply cut the filtration material provided in the kit to fit the vent grills in your rooms, placing the filter behind or on top of the grill.  As the air passes through the Allergy-Free Vent Filter media, both microscopic dust allergens and larger airborne irritants like moldspores, pollen and pet dander are captured.  The allergen particles remain on the filter rather than entering the room to trigger allergic reactions.