Cordless drill/drivers are best for most homeowners. The most common type of cordless tool, these use bits for drilling holes and driving or removing screws. An adjustable clutch regulates the torque, or twisting power, applied to a screw for delicate projects.
Cordless screwdrivers are good for light tasks. Lighter and more compact than cordless drills, these can replace your handheld screwdriver for many projects, but they aren't recommended for drilling holes or installing large fasteners called lag screws.
Cordless impact drivers are for heavy-duty jobs. When an impact driver turns, it uses momentum from the motor to deliver extra torque in a series of taps, striking about 50 times every minute. With about three times as much twisting power, you can use impact drivers for construction or mechanic projects for which a drill/driver wouldn't have enough power.
Single-sleeve keyless chucks can be tightened with one hand. Most drills have this feature or accept hex-shank bits that click into place. Some reviewers prefer an all-metal chuck, but some soft trim can protect surfaces from damage if your drill or driver slips. Some newer drills have chucks designed to keep tightening themselves as they spin.
Do you need one tool, or three? Cordless drills, impact drivers and screwdrivers are all designed to excel at one task. However, they can fill in for other tools as well. For example, a cordless drill can drill small holes, while some makers offer special hex shank bits that allow impact drivers to drill and saw like a cordless drill. Still, if you will be doing different tasks on a regular basis, it's best to buy separate tools for each one.
Try tools in person if possible. A good cordless tool should feel balanced, not front-heavy, as you hold it. The trigger should be responsive without being overly sensitive or difficult to depress. Be sure you can easily remove and replace the battery, too.
Consider a cordless drill combo kit. Experts say you can save money by buying a cordless tool kit that shares the same batteries and charger. If you already have cordless tools, your best bet might be to choose a combo kit (or individual tools) that use the same battery and charger platform.