I was trying to find a content oriented SEO plugin and so far Squirrly is looking better option to me. The best thing is this plugin searches keyword related contents like images and keyword related blogs, news, wiki info for you which really helps in creating a unique & quality contents. Using Squirrly for SEO is doing SEO with fun.
I have used All in One SEO and WordPress SEO by Yoast plugins but would not like to compare them with Squirrly because it plugin have there own specialty. So i would say test the plugin and decide it on your own which is best fit for your need.