We like the Beyond Guardian Air by Aerus because on top of the advanced HEPA filtration they incorporate photocatalytic oxidation, which cleanses water in the air, so this is ideal for humid climates where impurities can hang in the water vapour. For most climates in America this isn't really an issue but if you're in the Deep South, or if you have a moist basement, it can make all the difference. We also like the huge coverage the Guardian Air provides, covering up to 2,500 sq ft with a very quiet motor. This is a world class air purifier, though it may not be in everyone's price range. 

Highlighted features of the Air400:

• Coverage up to 2,500 sq. ft. (232 m2)* 
• Portable, no installation required 
• Uses ActivePure Technology® to reduce over 99.9%  

of many common contaminants in the air and on surfaces1 
• Features complementary technologies: HEPA Filtration, Activated Carbon Screen, and Photocatalytic Oxidation (PCO) 
• Energy efficient and whisper silent operation cleans 24/7 without producing ozone 

Conclusion:

In our testing we found the Beyond Guardian Air really lived up to it's promises of significantly reducing the contaminants and pathogens in whatever environment you use it in. It's portable and lightweight, has a very sleek appearance with a look of brushed silver, though the manual dial is pretty old-school and we were surprised the interface is so limited given it's price point. But it does what it says it will, unlike a lot of air purifiers that claim to clean the air but only blow it around. Since that's the most important aspect of our consideration for our top ten list, the Beyond Guardian Air ranks very high on our list. Our main concern is the high cost for it's PCO feature that may not matter much to most users.