Pick the articles for your niche sites very carefully to ensure that you are able to successfully get traffic and gain profit from these sites. If you are going to try and utilize free website content articles, then it may be difficult for you to find ones that have your exact keywords, so you may have to either make revisions to the articles (which may not be allowed on some free articles) or base your keywords on the articles that you find (which could leave you with very competitive keywords that would take a lot of time or money to attain a high ranking for). If you are going to buy content, make sure that you let the writer know what your niche keywords are and what your specific your preferred keyword density and placement are. Remember, the wrong articles can leave you with little traffic and very low search engine rankings if they do not fit in properly with either your niche or with keywords that are easy to attain high rankings for.