I have Purvac Barracuda now, but have had several brands in different homes. The important things I consider.
1. Get one with a disposable bag. It is cleaner, easier to empty, and protects the motor.
2. Do NOT get a contractor's special. It was inferior to a brand name and did not work as well.
3. You can get a power brush in two different methodologies. If electricity is supplied to the hose, a power brush with be activated by plugging it into the wall outlet. If no electricity, you can use an air-powered model.
4. To prevent marring the walls, especially around corners, buy a "hose sock" which fits over the hose and protects walls and furniture from abrasion.
5. New wans are expandable with the push of a button to reach the ceiling and under deep spaces. I really like this feature on my latest model.
6. If you put a hose outlet in the garage purchase a special hose so not to get the house hose dirty. Same thing applies to the basement.
7. You can hang the hose on a small plastic garden hose reel in a closet.