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.

saucecode

Minimalist Tag Cloud is a WordPress plugin that allows you to display your website’s most popular tags, categories or custom taxonomies as a widget or using a shortcode. 
The plugin styles the tag cloud in a minimalist style with the option to include tag count.
You can use Minimalist Tag Cloud as a widget or shortcode.
There are a number of options that you can customise:
<ul>
<li>number of items (tags) to show</li>
<li>type of taxonomies (tags / categories / custom taxonomies) to show </li>
<li>include/exclude a list of tags</li>
<li>smallest and largest font sizes</li>
<li>font size unit</li>
<li>display format (flat / list)</li>
<li>flat format separator</li>
<li>order by and order</li>
<li>show/hide tag count</li>
</ul>
Check ‘Installation’ tab for details on how to embed the shortcode.

Minimalist Tag Cloud

Very nice little widget. After looking through all the other tag cloud plugins this is the one I found most flexible.

It just needs a bit of styling on the way it displays on the backend. But it's not important. It does its job!

Thank you very much :D

Great customization!

Customisable widget and shortcode to display tag cloud with option to show tag count anywhere you want.

Jetpack Popular Posts vs Minimalist Tag Cloud