Will you be using it indoors or out? If you need a portable vacuum to clean items on your porch or deck, a corded model may require an extension cord. A cordless hand vac isn't restricted by cord length or proximity to an electrical outlet, but its runtime is limited, so it won't clean for more than 10 to 20 minutes, at best.
How long is your typical cleaning task? If your main cleaning needs take longer than a few minutes, a cordless hand vac could run out of power before you're finished. Either opt for a corded handheld vacuum or choose a model with a lithium-ion battery, which will run at full power until the battery is depleted -- up to 20 minutes, typically.
Do you have pets? Pet hair is difficult to remove from upholstery and carpets. Portable vacuums with extendable hoses, motorized brushrolls and rubberized pet hair attachments make pet-hair pickup easier.
How frequently will you use your hand vac? Some cordless handheld vacuums take up to 24 hours to recharge, though a portable vacuum with a lithium-ion battery will charge more quickly, in as few as 2 to 4 hours for some models.
What are your storage options? Most cordless hand vacs are accompanied by charging docks, which must be located near an electrical outlet for recharging, though others have removable batteries that can be powered up using a smaller charger. If your storage area lacks outlets and/or you don't want a handheld vacuum hanging on your kitchen wall, opt for a corded model which can easily be stored out of sight.
Handheld vacuum aren't expensive gadgets, unless you opt for a $200 Dyson. There are some ongoing costs to consider, however. Some hand vacs have non-washable filters that must be replaced every few months. In most cases, filters cost around $10 each, but this can add up for an appliance that only costs $40 to begin with. In addition, the batteries will eventually reach the end of their usable life and many portable vacuums either have non-replaceable batteries or the battery costs more than the unit itself. That may not be a concern if you're buying a $30 vacuum, just toss it and buy a new one every year or so, but it's something to consider on a more expensive model.