Depending on the purpose I work with WordPress or Drupal. Both are open source, both run on PHP and MySQL, and both are so widespread that hosting them rarely makes special demands.
Which of the two fits depends on what you have in mind, not on a preference. So here is what each of them is built for.
WordPress
The most widely used content management system in the world. It started as a blogging system and grew into a full CMS over the years.
What it brings: an interface editors find their way around without training, a large choice of extensions for individual jobs, from a contact form to a shop, and a theme system for a look of your own.
What it suits: sites that mainly publish, with a manageable structure and an editorial team meant to work on their own.
Drupal
In use for just as many years and with just as large a community behind it, maintaining extensions, called modules there.
What it brings: a modular construction that can be adapted a long way, an API-first architecture that delivers content without its own front end, and a permissions system that copes with complex data structures and many roles.
What it suits: projects with many content types, staggered permissions or an intranet behind them. Setting it up takes more effort, and its limits lie further out.
What I take on
The choice between the two, the setup, the adaptation to your editorial team, and moving existing content across.
And afterwards the running of it: updates, backups and introducing the editorial team. Consulting, prototype, delivery and upkeep come from one hand if you want them to.
What I advise against
A CMS for a site that never changes. And deciding on a system before it is settled who will look after the content later. A tool nobody operates costs more than a page built by hand.