FESTOOL

Best of the Best: Festool

I could go down a very long list of what makes Festool drills different. They are a product of German engineering. They have interchangeable chucks. They have brushless motors and an electronic clutch. Their batteries are backwards compatible. But what you need to know is that Festool products are in a class all of their own. When we talk about the best cordless drill we have a certain price in mind. For that reason Festool generally doesn't get to compete in those categories.
Festool 564250 T 15 + 3 14.4-Volt Lithium-Ion Cordless Drill/Driver Kit
Brushless Motor

Festool drills are the only ones I know of that use brushless motors as opposed to brushed motors. (I had read somewhere that Panasonic uses brushless motors, but their specifications say otherwise.) If you want a more technical explanation of why brushless motors are better you can read up here. The short explanation is that brushed motors have brushes which make contact with the rotor as it spins. The friction slows down the motor and creates heat. So it's not surprising that brushless motors can last MUCH longer.
Interchangeable Chucks

The drill in the picture above is the Festool T15 + 3. As you can see it comes with three chucks. It has a regular 1/2" keyless chuck like other drills. The "eccentric" chuck let's you position where the bit is. It can be at the top, bottom, right, left, or any of the 16 positions. This lets you get into tight spots. And then it also comes with right angle chuck. That's right, it's also a right angle drill.
Electronic clutch

Most drills have physical clutches. In many cases physical controls are better than electronic, but not with cordless drill clutches. Physical clutches allow a certain amount of torque and then slip. That's wear and tear every time you use it. The drill is also working against itself, since the motor is putting out torque and the clutch is holding it back. With an electronic clutch, the motor only puts out as much torque as is needed. There's no extra wear and tear.
Backwards-compatible batteries

Festool has moved to higher energy density lithium-ion batteries like all of the other top drill manufacturers. But Festool's drills allow you to use the older batteries as well. This isn't surprising because Festool drills generally last much longer, so once you buy into the system you generally get to use your old parts. You can even use older NiCd batteries.
Best of the Best

Festool drills are in a class of their own. There are no other drills that even come close to the features, precision, performance, and reliability of Festool drills. But they also cost over twice what other drills cost. But you can expect them to last longer too. But if you want the absolute best cordless drill, then you want a festool: