Kind of User
A power tool is an extension of your hands, like Edward Scissor Hands. If you have the right tool and a quality tool, you can create or fix just about anything. One important questions you need to ask yourself is, "What kind of user am I ?"
If you are a light homeowner user, you can get away with a less expensive brand such as Black and Decker. A light homeowner user probably will not put a lot of use and abuse on the tools and power is not a big deal. Remember more power usually means more weight in the tool. Black and Decker designs their tools for the light homeowner use. They are quality built and inexpensive.
If you are not a light home owner use, but aren't a serious user, Craftsman makes an exceptional tool. Craftsman actually has other companies make these tools for them, you can see their manufactures through the source code. Craftsman makes a good quality tool that has a lot of features and good power. Plus they have a great return policy if something happens or you are dissatisfied with the tool.
If you are a serious home user or contractor, go with a good brand name such as Milwaukee, Dewalt, Bosch, Porter Cable or Makita. These manufactures pride themselves on making the best tool. They are constantly putting money into their research and development process to make these tools even better. These professional power tools cost more, but they are made with better technology and materials. They also have a better design that causes less fatigue on the user. Not to mention that these tools are made to last a life time.
The tools mentioned above are good quality tools. I would suggest staying with one of the manufactures above for a couple different reasons, but the main reason is efficiency. These power tools will last you a lifetime. They are designed by companies who have been in the business for along time and they understand power tools. They understand quality, safety and what makes a good tool. These are more efficient meaning they can actually transfer more power from the input or batter to the output. This means less work for the user and less frustration. If you would like to learn more about the difference between cheap power tools and professional power tools, please see this article.
Corded Vs. Cordless
Corded power tools tend to have a little more power, while the cordless has the versatility. At least this is the case now. Milwaukee just came out with a new battery technology that might change everything. Cordless power tools are becoming more and more common as they are increasing their power, while lowering their overall weight of the tool. I would suggest going with a cordless tool because of versatility. The only reason to go with a corded tool is if you will be using the tool for long periods of time or the tool you are looking for has a substantial more power capability in the corded version.