First of all, it has to be an apple to apple comparison...can't compare air stone with downdraft or venturi..right? Comparison has to be made within same category...for example, for HOB..you can compare deltec MCE series with CPR Bak Pak, Reef octopus HOB, aquamedic turboflotor, aqua C remora, red sea prizm, etc...to name a few. Then cone models, you should compare between skimz, reef octopus, bubble king....