I only have some second hand experience to offer here.
My mom tried several brands a number of years ago (so the new ones might be much different), but don't choose anything with a disposable filter. They cost a lot to keep buying, and tend to become unavailable over time.
I had a very small and inexpensive unit once, and honestly, I don't think it did much. I felt the same way about the more expensive ones my mom had as well.