Done a lot of research and so far this is the best.I have 2 kids and both have allergy problems.After buying product my kids haven't coughed at night like they used too.
Its very energy efficient so i run the thing 24 hours.The only draw back is the price of the replacement filters .But if you have allergy problems thats the least of your concern and you only replace the HEPA once a year and the charcoal once every 3 months.
I personally dont think you should change the charcoal filter every 3 months unless you smoke in the house or have alot of pets.
For the money I highly recommend this one dont get fooled by other type of air filtration such as ionizers.They somewhat work but at the same time causes ozone in the air that can cause lung irritation for some people that is really sensitive.
Consumer report rated this model fairly high and i took their word for it and no regrets so far.I've had this for 3 months now and i actually ordered another one for my bedroom.
And my last advice is that if your room is... say 100 square ft.Get the filter that is rated at the least 150 square ft preferably more.

Recommended: Yes

Amount Paid (US$): 218
Battery Life: N/A
Noise Level: More quiet than most