Wordpress is the most commonly used CMS, followed by Joomal and Drupal.
From a security standpoint, I would suggest thinking about flatfile CMSes like Hugo, Grav. These are easier to maintain as you only push html files.
I agree with @bountysite and @castordor, I am still using Wordpress for all my sites and feel great with this cms and not going to change to another cms at least some next years.