If you have a large house to vacuum, or would like to vacuum the stairs in one go, make sure your new vacuum has enough hose and lead length. It's rather frustrating when your vacuum won't quite reach into the corner and you have to go back to the power point and replug into another one.
Vacuums with ample reach will need to have a cord length of at least six meters and a hose length of at least four meters. If the cord length is any less, you probably won't reach the top of a standard flight of stairs, unless the power point is nearby.