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.
Although many people aren't aware, upright and cylinder vacuum cleaners were originally designed for different purposes. Upright vacuum cleaners were designed for vacuuming carpeted floors in cooler climates (such as the UK) while cylinder vacuum cleaners were designed for vacuuming hard floors in hotter climates (such as Spain). As a result, not all cylinder vacuum cleaners come with powerful rotating brushes.
Not all bagless vacuum cleaners are the same. The type of separation system makes a big difference to the performance of the machine and the amount of filter maintenance required.