It is recommended that you use unique content at all times. Most search engines, especially Google, supports quality, rich content articles. Just to give you an example, my clients always order between 10 and 20 different articles, with different keywords. They request for each article to be unique. Obviously there will be some overlapping information, however, the Google search spiders, analyze word usage, sentences, paragraphs and content in general. Your article must be informative and well written, in order for it to perform better with search engines. So, I recommend that everything you write is unique, yet, you are still providing the same information.