LordPretender

Similar to the original native one, this plugin let you define the range of stats to retrieve. 
Also you will be able to add the category name of the post.
Finally, this widget will only display posts (and not pages too). 
This plugin read the top 100 of posts/pages and keep only the X first POSTS (X = number defined in the widget parameters). So, you can have less posts than requested.
Jetpack is required to work. 
A wordpress account and your blog must be linked.
You can find a demo here : http://www.spoils.fr/ 
The widget is named “Articles populaires” on the sidebar.

Jetpack Popular Posts

Using Jetpack stats, this widget will display the most popular posts.

gdthemes

A very simple popular posts widget which displays posts by comment count (with featured image).
This is a very simple plugin which displays your posts by comment count when activated at your desired sidebar. 
It comes with a setting whether you’d like to display your post’s featured image or not and also be to adjust the width and height of it.
No CSS styling has been done and it is up to you to customize it.
Please write a review or rate if you like it! 🙂
<h3>Upgrade</h3>
<ol>
<li>Use the plugin updater in WordPress or…</li>
<li>Delete the previous <code>my-popular-posts-widget</code> folder from the <code>/wp-content/plugins/</code> directory</li>
<li>Upload the new <code>my-popular-posts-widget</code> folder to the <code>/wp-content/plugins/</code> directory</li>
</ol>
<h3>Usage</h3>
<ol>
<li>Just install and activate.</li>
</ol>

My Popular Posts Widget

A very simple popular posts widget which displays posts by comment count (with featured image).

Jetpack Popular Posts vs My Popular Posts Widget