As per the data released by BuiltWith, WordPress is the leading CMS with 43.68% in top 100k Sites & 51.59% in top million sites, followed by Drupal with 12.16% in top 100k sites

Number of sites powered by respective CMS:

As far as usage is concerned there is no threat to WordPress in the near future as the number is growing real fast and the competitors are way behind to be a threat to WordPress in recent time.

The popularity of WordPress as content management system is because of the user friendly management system and the huge community behind this great CMS constantly producing amazing products for WordPress.

Also, the word of mouth from WordPress user always being positive encourages new users to take up WordPress as their first choice.

Data Via BuiltWith