Be wary of "HEPA type" and true HEPA filters...

http://www.air-purifier-power.com/hepatypefilter.html

I have a Winix U300, and it has worked reliably for a couple of years:

http://www.amazon.com/gp/product/B00KXV8KIK

You might want to consider the WAC9500, however. I don't recall why I made the decision to buy the U300 over this model:

http://www.amazon.com/dp/B004VGIBZK

Folks that are super serious about filtering allergens and viruses tend get the IQ HealthPro Plus, but it costs nearly 900 USD:

http://www.amazon.com/gp/product/B002VXDCHW