Some time with the winix c545, now, it has a 3watt mode and a 4 watt mode, the levoit 100s and c300 goes down to 5 watt and 6 watt.
The winix with its much bigger impellar is throwing more air. I am confident of that at this point.
Horizontal units are also more quiet, they seem to uniformly run at lower rpm.
Can't escape ball bearing sound if you got it close to you, it's all ball bearing.
The only disadvantage of the 545 is it has a very small filter for its size, the older version 535 had a filter 50% bigger. as is the new 555 and 5300/5500.
Those are made in korea, while the 545 is made in thailand.
Does that really matter, at the price, given that you do get a pretty big motor overall. I suppose not. Smaller filter size does mean lower efficiency. This I'm not sure is a problem except for people that live in long extended fire/smoke seasons.
I would recommend people buy the larger 555 or 5300 units instead of the 545. The app is also down at the moment, won't even work, so they're clearly not the best software team.
If going levoit which are better looking than winix, I could recommend the 100s and their larger 200s unit. But winix seems to go on sale more often at costco.
The vertical units, if it suits the room visually, and foot print, go for it, but Tp4 is quite sure that they're a bit louder even at the lower modes. more turbulent wind noise because of the dual air guide and higher rpm throughout using a smaller impeller.
One suspects these units can definitely overheat if the filter becomes too clogged. the motor is dependent on adequate airflow to cool the hub.