I have a Festool vac in my shop...
My favorite vacuum for cleaning the house is a backpack-style vacuum like they use in office and commercial buildings. It is called Pro-Team and I got the Super Quarter Vac with HEPA filtration.http://www.pro-team.com/vacuums/default.aspx?style=1
I love this vacuum. With a 50 foot cord and a fairly light backpack with well-padded shoulder and belt straps and I can move quickly through the house without having to drag a heavy canister or upright, or constantly plug and unplug the cord. It is a breeze to clean steps as you walk up (or better down) them. It's also no problem to put on a brush attachment and periodically clean all the high places -- window sills, above door jambs, the tops of tall furniture, etc.
I can vacuum the house in 1/3 the time it takes with a canister vacuum, and the suction is fabulous.
My wife and housecleaner refuse to use it. They won't strap on the backpack.
That's a pretty big con...
Also, you have to get used to having something on your back so you don't bump into furniture but you figure that out pretty quickly.