I just purchased an air purifier for our bedroom, but it hasn't arrived yet so I can't give firsthand comments. After doing quite a bit of research online, I concluded that Rabbit Air is probably the best right now. They have two different models, each of which comes in two different strengths. The one I finally decided on is this one:
http://www.amazon.com/Rabbit-Air-Bio...dp/B00GH19UW0/
I purchased directly from the RabbitAir website, as I could see no advantage to purchasing this particular item through Amazon. The RabbitAir website has a comparison chart of their different models that I found helpful:
http://www.rabbitair.com/pages/choose-your-air-purifier
One thing I like is their 5-year warranty which covers shipping both ways if a unit needs repair.
Several years ago we bought a larger, circular Hepa air purifier from the local big box home store. It worked too, but was too noisy for my husband at night. This time I wanted something that was smaller and more quiet.