In my experience, using them for pollen, buy the largest ones and you can run it at the lowest level so that it's quiet and the filter lasts the longest. I've

In my experience, using them for pollen, buy the largest ones and you can run it at the lowest level so that it's quiet and the filter lasts the longest. I've had the Kenmore-branded version of the Whirlpool Whispure AP51030K. I see some suggestion that the newer ones since they sent production overseas are a bit lesser quality, but the price is certainly less than I paid a decade+ ago. Nice feature is that there is a separate replaceable pre-filter for dust. 3M used to make some, but discontinued them. I have a couple of those. Honeywell also makes some decent ones, though I haven't used them personally. Unfortunately I've not seen anyone making a HEPA filter that uses standard-sized furnace filters, which is unfortunate because the better versions of furnace filters (e.g. 3M filtrete "purple") are about equivalent to HEPA filters and usually cheaper. The discontinued 3M air purifiers used a different size, I suspect to keep up a razor-blade business model :/ On the other hand, if you have forced air heat/ac (I do not) and if you use the better furnace filters you might be fine just running that (including a fan-only mode if possible).