The best replacement for air filters is stock air filters.

The best alternatives to air filters are rated as following:
★★★★★  stock air filters
★★★★  oiled
★★★★  k&n
★★★  3m air filters
★★  media air filters
★★  air purifiers
★  furnace filters
★  purifiers
  disposable air filters

Your alternative for air filters is not listed? Suggest!
Speaking about air filters, one probably shouldn't forget about humidifiers.

Other search terms related to air filters and their ratings are:
★★★★★ humidifiers
You have in mind a companion for air filters and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of air filters in all years. Click on graph for more.
air filters
stock air filters
oiled