Nader

The “Most Comments” plugin displays as the name says posts with the most comments. You can either use the widget in the sidebar or integrate the plugin as template tag in your theme files.
Features:
<ul>
<li>Limit the amount of posts to be shown</li>
<li>Show comments from a specific post category</li>
<li>Exlude posts without comments</li>
<li>Select a time range (last XX days) of posts to be taken into account</li>
<li>Customize the design template via the settings page</li>
<li>Place a widget in your sidebar</li>
</ul>
More Information & Feature Description: 
http://www.brandinfection.com/wordpress-plugins/most-comments/
<h3>Configuration</h3>
You can configure the most comments plugin to your needs. Options can be found under the menu <code>Settings > Most Comments</code>

Most Comments

Display posts with the most comments, as a widget or on a page using the template tag. Customize the look with specific settings.

ProRankTracker

Pro Rank Tracker® is a cutting edge ranking tracking tool (SERP Tracker) for keep you up to date with all the latest changes on the rankings of your websites and videos.
If you don’t have a PRT account yet, you can sign up on: http://proranktracker.com
Why choose ProRankTracker software ?
<ul>
<li>Next Generation rank tracking technology </li>
<li>Amazing affordability (including a free plan)</li>
<li>Unbeatable Accuracy tracking across a huge array of search engines</li>
<li>Powerful local and mobile rank tracking options</li>
<li>Enterprise-level white-label reporting to clients solutions</li>
<li>Easy access anywhere, anytime from web and mobile apps</li>
</ul>

Pro Rank Tracker

I make that only on very few occasions to give a bad feedback, but this here deserve it - my recommendation, save your time, don't download it - it does not work at all, at least not before you not pay - and there is no chance to find out / test it ...

Pay befroe you try

Using ProRankTracker's Wordpress plugin, you can view your wordpress site's rankings and stats from your PRT account, directly on the admin  …

Most Comments vs Pro Rank Tracker