First are you a light sleeper? some ppl cannot have one in the room, some prefer it (white noise)
I'll just tell you the one i have arrived at (after 1,000s)
Amazon.com - Winix WAC5500 True HEPA Air Cleaner with PlasmaWave Technology - Hepa Filter Air Purifiers
This is the one in our bedroom, my wife has allergies and it's considered one of the best ones for that.
at the basic level you have the carbon pre-filter, this will help with air quality, make stuff smell better (or at least take the odor out)
Then you have your standard HEPA filter, this is where all the allergens/dust crap gets collected.
Then it has some kind of plasma thing that kills bateria like ozone, w/o making ozone.
It's hyper sensitive, we have it "auto" and whenever my wife opens nail polish or, some type of facial cleanser, it kicks up to turbo cuz it smelled something, which is cool, cuz i have never seen anything react with this much sensitivity. (usually only smoke does that for most air cleaners)
our house is split into 4 quads for tenants, either our neighbors are using some funk, or the house just gives off stuff, cuz when we visit their apartments (well 1 neighbor, we don't give a shit about the other 2, they old ppl anyway) her allergies kick up.
If you don't need something so grand for allergies, a good honeywell (usually known as the drum type) will do a good job with dust/air cleaning, some allergens.
Amazon.com - Honeywell 50250-S 99.97% Pure HEPA Round Air Purifier - Hepa Filter Air Purifiers