I’ve tried almost all of the major WordPress SEO plugins on the market and one of them seems to reign supreme. Yoast’s SEO.
The Depth and breadth of Yoast’s commitment to this plugin is remarkable, and he continues to give it away for free. Others have gone so far as to blatantly plagiarize his code in an attempt to commercialize it because they know they can’t come up with a better alternative. My reasoning here.