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.
Wattage is an important consideration because motor power alone does not guarantee better suction: it depends on the overall design of the unit. If a vacuum cleaner has a high wattage, the motor is more powerful.
An upright vacuum cleaner has a vertical dustbin. In contrast, a cylinder vacuum cleaner has an almost horizontally positioned dustbin. Unknown to some, these two styles of vacuum cleaners offer both advantages and disadvantages. You should base your overall choice on the area you will be vacuuming and your individual preferences.