What is the best content relevancy and optimization tool?

It's a bit pricey, but I like Scribe (http://Scribecontent.com) by Copyblogger.  I particularly like it because of some of the educational perks, like the Authority (subscription that comes with it (I assume they still offer it free with Scribe).  Also, it's by a company that lives and breathes copywriting/content marketing.

Scribe is available as a Web app, a plugin for WordPress and Joomla!, and as an add-on for MS Word on both Windows and Mac.

I've used InboundWriter and a few other a couple of years ago but decided to stick with Scribe.  As a caveat, I don't do as much writing as some, but I do enough to make Scribe worth having.  The simplicity, perks, and convenience make it worth it.

Hi,
SEOPressor may be your best tool. It has a content grading feature, optimization suggestions, as well as other WordPress optimizations like Twitter Card, Facebook OG tags, Dublin Core and more. It also suggests LSI keywords to help improve overall content relevancy. Many bloggers and content marketers are using SEOPressor.