The biggest, single best advice most vacuum professionals will give is to use a machine that uses vacuum bags as opposed to dump-out bagless machines. When a machine utilizes vacuum bags it's usually the first sign of a quality vacuum.
But vacuum bags are expensive and its just one more thing I have to buy.
Yes, it is one more thing to buy, but a single bag lasts much longer than most people think. For example, in the picture below the bag being thrown away contains approximately 20-30 of the bagless empty-out bins on the right. This is because everything is compacted into a vacuum bag as opposed to just floating around a cup.
The average lifespan of a bag for pet owners is 3-6 weeks. Most packs of bags cost between 10-20 dollars for 6 bags. One can expect to use 1-2 packs of bags a year!
So, two packs of bags a year! Thats about $40 a year! What about filters?
This is where the cost and health benefits heavily favor bagged machines. The vacuum bag is the first filter in a vacuum, it captures most all of the debris, this way the HEPA exhaust filters can focus on further cleaning the air. Bagless vacuums usually have at least 2 filters. Some companies claim they are washable but for the sake of odor and proper filtration, they are not, or, should only be washed once or twice before replacing. It is the industry's best advice to change filters in a bagless machine every 6 months. This is very costly. These filters usually cost between $40-75 for the set. Twice a year, thats $80-$150.
We will delve deeper into what true HEPA filtration is in a later entry.
For more information regarding bagged vs. bagless check with credible online sources like "Allergy Buyers Guide" and "Allergy and Air".