Cord length Make sure that the cord is long enough for you to effectively clean one area of you home without having to change outlets. The roller with bristles under the machine that spins when the machine is on. It increased the cleaning effectiveness on carpets. Some models have vacuum areas that extend to the edge of the bottom of the machine for cleaning tight edges. Other Tools Detachable hose, extensions, upholstery brushes, corner cleaners.
Some units have caddies to hold all the tools.
Some models have lights at the front of the base. Unless you live in a particularly dark home, this feature is more of a novelty than a necessity. See Consumer Reports for comparisons of different models. The above is intended for education purposes at the starting point of the vacuum cleaner buying process. It is not intended to be an all-inclusive description of how to buy a vacuum cleaner.