Vacuum type mostly comes down to how you'll actually use it — the specs matter, but not as much as picking a shape that fits your home and habits.
The three main types
Upright vacuums are a single push-forward unit, generally offering the strongest suction and largest dust capacity, and are well suited to homes with mostly carpet. They're bulkier to store and less agile around furniture and stairs.
Canister vacuums separate the motor unit (pulled along on wheels or carried) from the wand and hose, making them more maneuverable for stairs, upholstery, and getting under furniture. They tend to be quieter than uprights but are an extra piece to store and drag around while cleaning.
Robot vacuums clean on a schedule with no one holding anything, which is the whole appeal — but they have smaller dust bins, generally weaker suction than a plug-in vacuum, and can struggle with thick carpet, cords, and cluttered floors. They're best thought of as a maintenance layer between deeper manual cleanings, not a full replacement for one.
Suction wattage is a weaker signal than it sounds
A vacuum's motor wattage measures power draw, not actual cleaning performance at the floor — how well that power translates into suction depends heavily on the nozzle design, airflow path, and how well the machine seals against the floor. Two vacuums with identical wattage can perform very differently in practice. Independent cleaning performance tests are a far more reliable comparison than the wattage number alone.
Filtration matters for allergies
If allergies or asthma are a concern in the household, look specifically for a sealed HEPA filtration system, not just "HEPA filter" on the box — a HEPA filter only helps with allergens if the whole vacuum is sealed well enough that air isn't leaking around the filter rather than through it.
The one thing people forget
Check the cost and availability of replacement filters, bags (if applicable), and brush rollers before buying, not after the first one wears out. Ongoing consumable costs vary a lot between brands, and a cheaper vacuum with expensive, hard-to-find replacement parts can cost more over a few years than a pricier one with cheap, widely available parts.