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.
For many years people used article spinners to mass produce unique content from one source article without really thinking about the quality and the human-friendly flow when it came to a real human having to read the content they landed on when visiting the website. Much more emphasis was put on producing content that was purely made to fool the search engines and rank the website accordingly.
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)!
Spin Rewriter integrates with almost any SEO software. This allows you to post high quality articles quickly and easily. The only drawback is that you only get something like 300 API requests every 24 hours. You can quickly burn through this if you’re doing multiple campaigns. The developer does not currently offer a plan for heavy API users but maybe they will in the future.