Q.   What kind of vacuum cleaner should I buy?

Short Answer: An Upright Vacuum with HEPA filtration that you are comfortable using on a daily basis.

Long Answer:   2008 brought a lot of very good vacuum cleaners to the market. Now in 2011 the prices have come down to the point where $200.00 will buy the power and filtration you need.  Make sure the vacuum you chose has a true H.E.P.A. Filter.  These filters are very important because they limit the smallest particles from being redistributed back into the air that you and your family are breathing.  True HEPA filters cost the manufacture more so watch out for deceptive terms like "hepa style filter". 
A quality upright vacuum cleaner is going to weigh at least 15 pounds.  Some models however weigh as much as 25 pounds.  It is important to accurately judge your ability to push the thing around your house.  A Vacuum that is too heavy for the user will not get used.  The best way to find out how it feels, is to go to a store where the Vacuums are available to turn on and use.  Commercial carpet a store does not provide as much friction as a residential carpet, so use one of the lower settings to approximate the conditions of your home. 
A common mistake that people make with Vacuum cleaners is setting the height adjuster too low.  This causes the brushes to dig in to the carpet and slows down the motor, which decreases the airflow on all single motor Vacuum Cleaners.  It also can cause unnecessary wear to the carpet fibers and Vacuum brushes.  Adjust the height of the Vacuum so that the brush is making contact with the carpet but not much more.  Over time as the brush wears down, you will need to lower the height adjustment to compensate.

Delta Steam-Way
The Premier Carpet Cleaners in Elk Grove