I worked at the Home Depot for a while and when I started had used many before but never really bothered to check out what brand was what and which were the best. Probably because I had never purchased my own and always was borowing from dad or using them at work. So when I started getting specific questions about drills, I started really checking out what each brand was doing and what market they were going for.
I'm often going to generalize a little to avoid having to write a 50 page article. First to pick the right tool, you need to know what you're going to do with it. Once you've figured that out, it helps to know what brand is in your price and professionalism range. If you're going to drill screws into drywall once a year, please don't bother wasting your money away.
Light-Duty Occasional Users
Ryobi: the affordable tool for the occasional user. My father-in-law has a Ryobi that was passed down to him from his father. Don't expect that kind of durability with their newer tools. They're inexpensive and for a good reason.
DeWalt and Makita are great medium to heavy-duty drills. I've had a bit more product returns on deWalt, but they're comparable. These are for the average joe who wants dependability without paying an arm and a leg for it.
Heavy Duty Pros
Bosch, Rigid and Milwaukee are definitely the cream of the crop. You can typically feel it from the moment you grab them. They feel heavier and much more robust that the other brands. This is what the guys who work with power tools all day will buy. If you can afford them, go for it, you just might give them to your son or daughter when you leave this world.
Cordless or Electric: Ever notice most stores never have sales on drills that electric ? Always discounts on the battery operated ones, and do you know why ? So that you won't take the time to pause and think, and realize that unless you absolutely NEED a batteries and you're working in an area where there's no electricity, it's a sham !
Batteries are often sold for almost the price of a new drill. They last a maximum of 5 years and then you're stuck buying a new expensive drill since the batteries cost too much. The deWalt 18 Volt XRP Battery is currently sold at Home Depot for 149.00$ That is insane. If you can avoid it, simply buy a plug powered tool and buy an extension cord instead.
Impact, Hammer Drills. Find out beforehand if you need your drill to be an impact drill and driver or simply a hammer drill. There IS a difference. An impact drill will give pushes in a torque wise direction, allowing you to put in screws into practically any material. A hammer drill, on the other hand, is typically used to penetrate concrete and the like. It gives hammer-like hits so that your drill bit will bite into the masonry you're trying to drill.