When you are using a drill at many different locations, it's a real pain to have to drag a cord around with you. At first, cordless drills weren't very robust and the batteries didn't last that long. For a while, that was an excuse for woodworkers to resist the change to cordless. Today's cordless drills, especially in the 18 volt class, are both powerful in terms of torque and their lithium ion batteries are long-lasting. The chargers are high-speed and so, with two batteries to swap, it's hard to run out of electrical energy.
So, where do different designs of cordless drills stand apart from one another? Actually, in several areas, the most important being tool weight and twisting power or torque. It used to be a rule that if you wanted more muscle and/or longer battery endurance, you had to accept heavier tool weight. While this is still factual, in a general sense, important inroads are being made by major drill designers to turn this equation around.
Tool weight is of great consequence in a drill or impact driver because these are tools that you extend at arm's length all day and while 5 to 10 pounds may not sound like much, each weight increase from drill to drill counts for a lot at the end of a long day on the job even if your name is Hercules.
Muscle is important because drills are often used to drive screws even though there is a better tool for that job: The impact driver. Most 18 volt cordless drills come with half-inch chucks and if you have ever drilled a deep 1/2' hole in hardwood, you know the need for power. You might even find yourself driving a large Forstner bit which is a lot more than 1/2'. You don't want to buy a drill that will be weak on the job.
A drill is the kind of tool that a woodworker uses recurrently and so it is important to investigate to make sure that you are buying the right one for your requirements. Battery size, expressed in amp hours is another key consideration. All lithium ion, 18 volt batteries are not alike in terms of size, heaviness or how long they will keep going between charges. That goes for chargers, as well. A half-hour charger, as opposed to an hour charger can make a real difference if you are always alternating batteries.
When you contrast the brands, you will see that drill muscle power and drill weights are all over the place. So are the price tags. You can economize by buying factory-reconditioned tools but don't acquire an underpowered drill with a small battery just to save money. Don't purchase an overweight drill just because it has a bit more torque than its lighter competitor. Get the drill you really need. You will thank yourself later.