Think of it this way: What do you have more chance of hitting, a distant, tiny target or the broad side of a barn? For the sake of search engine optimization, you want your website to be the broad side of barn. The more quality articles, or unique readable content, your website or blog offers to search engines (and therefore the general public) the more exposure your website will receive from major search engines.
Quality readable content is key here. Google, for example, will recognize that people are leaving your site soon after arriving if they perceive that your site or blog is full of junk content. This is called "bounce rate." If your bounce rate is high, then people are quickly leaving your site. But for the sake of your business, to build your online reputation and brand, you want people to visit your site, stay for a while, and then keep revisiting over the long term.
Seriously noone has mentioned Unique Article Wizard? Check it out it blows the other 30 or so article writers I've tried out of the water. It contains a synonym database updated by users so the synonyms actually make sense and are available for entire phrases as well. There is no magic pill that lets you click a button and bam you have a new unique article. That doesn't and will never exist so stop lookin if you are(or squander your hard earned $ on failware)!
SpinReWriter is a handy tool which helps you in spinning your original content with randomly created phrases and words with substitutes. In addition to it, these tools have many advanced features and functions which smartly turns content error-free. Its powerful performance uses algorithms to entirely modify the articles into a copy that has been never posted before.