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.

Nick Momrik

Add a widget to display a list of the posts/pages with the most comments.

Most Commented Widget

Add a widget to display a list of the posts/pages with the most comments.

Jetpack Popular Posts vs Most Commented Widget