vacuum cleaner

You didnot mention the vacuum cleaner is for household or
industrial uses. I assume for household use.
You consider the air quality is most important, then you can ask to
have the exhausted air comparisons in each model. In their specs,
look for the particle size of the exhausted air, the smaller is the better.
However this will also reduce the suction power a bit! Also you
need to choose a power brush if your house is fully carpeted.

2008-11-24 15:27:58 補充：
Regarding the price for household,item#4 is too high, what is horse power of this item?
What is the reason for a household vacuum cleaner to cost over ten thousands. If you need
a high suction vacuum cleaner, it must at least 2 H.P.But higher H. P. means higher noise.

2008-11-24 15:32:43 補充：
Item#2 is most compatable. I like vacuum with bag because the dirt & grim are localized
in a fixed place. For bagless & water filter, you need to clean the cabin too. I have not
sold vacuum for mroe than 10 years, make your own judgement.