It depends as there is a tradeoff. At higher MERV ratings, you block more unwanted allergens. However, the downside is that you also restrict air flow and reduce air circulation which can have the unwanted consequences of less comfort in your home and possible damage to your unit. In general, a MERV 8 filter is sufficient to block common allergens like mold spores, pet dander and pollen. If you have bad allergies, a higher rated filter along with other indoor air quality products can really improve your symptoms. Ask your Air Flow Designs Rep for customized recommendations for your specific needs.