Ask what size vacuum is best for your house. Make sure you have enough room for convenient storage.
Is the unit capable of vacuuming wet spills? Some vacuum cleaners will suck up dry particles and liquid, with a separate setting for each.
Barrel or stand-up?
Which do you find easier to operate? Will a stand-up model fit in your cupboard? Make sure that you choose a design that suits you personally (or whoever will be cleaning the house!).
How effectively does the vacuum convert electricity into airflow? Will it be powerful enough to penetrate deep into the carpet?
Does the vacuum have adjustable power settings? Will it work on delicate material, such as curtains, etc.?
Can you reverse the airflow of the vacuum? This is handy for directing dirt particles into one area and clearing a clogged nozzle.
Is the dust collector reusable or disposable? If disposable, how much are replacements? If reusable, is it easy to remove and reattach?
Does my house attract excess dust? Is it hard to remove it from my carpet? A turbo head will prove more effective at removing dust and dirt than a regular vacuum head.
Is the electricity cord contained within the unit's casing? Is it long enough to get from room to room or do I need to plug it into different outlets? A long, retractable cord will make cleaning quicker and easier.
How loud is the vacuum? While few vacuums can be classed as quiet, some are a lot noisier than others.
Is the vacuum unit easy to carry or move around? Do its wheels respond fluidly? A poorly designed or unwieldy vacuum will make your job needlessly difficult.