What Travel Guide Books do you often use? what makes it great?

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I mostly use Lonely Planet guide books simply because I'm used to their format. I also have the Insight Guides but these are mostly what you read before going to a certain place because they place more emphasis on the history and background of the place rather than recommendation. DK eyewitness is also great because it's illustrated and in color so you get to see what the place looks like. Then again these are also intended for reading before the actual trip since it's kind of heavy to bring along. Can you share your favorite guide books and why do you like it?