There are two open source php CMSs worth considering for a web site: Drupal and eZ Publish.
Since its version 5.0, eZ Publish is based on symfony. It is really powerful but its content structure is somewhat rigid, it is less customisable than Drupal.
Drupal uses some symfony components as well for its latest versions, but it is not a real symfony application like ezpublish. Its power is its versatility: It can do anything and everything.
It has a big community and some great modules and some horrible ones. You need to know what you want to do before you do it, because it is really easy to lose yourself in your own developments.
You can organize your content as you like or not at all.
Wordpress... As hard as it tries to be, wordpress is not a cms. It is a blog engine that can be hacked to do horribly the job of a cms. Its codebase is horrible.
A number of features heavily depend on the theme you use, which is an abomination. It is widely used and, as such, heavily targeted by hackers. There seems to be a new exploit every other day.
I have worked with Joomla a lot, but it was several years ago, between v1.2 and 1.5. I don’t know about recent versions, but it was a mess. You could not define different content types. Your site structure had to have 3 levels (2 leveles of categories, 1 level of content), no more no less.
You couldn’t define additionnal fields for your content. It had huge security flaws. Extensions couldn’t work with each other (for instance, there was a widely used extensions to define groups of users, and another one to define permissions. As they didn't work together, you couldn’t give permissions to a group of users...).
With wordpress and Joomla alike, you have to design your site for what it can do. WIth a real cms like eZ or Drupal, you design your site first an then you adapt the cms to do what you want.