I've owned a bunch of air filters but I like the IQAir ones the best. IQAir machines are built around a very heavy-duty prefilter that traps all the hair, dust, and large particles (maybe pollen-size?). The HEPA filter thus only gets a stream of tiny particles, so it lasts quite a while. Other models I've used (Plasmacluster, Rabbitair) do fine with brand-new filters but quickly accumulate dust that you have to vacuum out, and even then, the HEPA filter is probably already ruined. They also aren't sealed as well, so you don't get to hold up your particle counter to the exhaust and see a nice "0". (But the particle count in the room does decrease versus not running them, so they do do something.)

The IQAir machines don't need any maintenance other than buying new filters when it tells you to. If you are trying to save money, don't buy IQAir.

I try to evaluate effectiveness qualitatively and quantitatively. When I first got an air filter for my bedroom, I noticed that suddenly I didn't feel like coughing all night long. When I got the IQAir for my bedroom, I woke up the next morning with a sore throat because the back of my throat was totally dry. My chronic post-nasal drip was gone. It could have been my imagination, so I bought a laser particle counter to measure the particle count in my room. It was 0. (And it's counting the sub-micron particles.)

(There are some caveats. Moving around in bed is particle city, so you're not breathing 100%-fresh air all night. But the filters take care of things very quickly, and I run them on a high setting, and they're close to my bed. You'll need earplugs. Air filters on the "silent" setting do approximately nothing. This was not a problem for me because I've slept with earplugs for years due to annoying cats. Now I can't sleep without them, the sound of sheets moving against each other is annoying :)