Wordpress and Zend are two very different animals. In a nutshell, Wordpress is designed for creating blogs, and with some plug-ins, custom coding, and a bit of coaxing can be made to go beyond just blogs. In a similar vein would be Drupal or Joomla, being for more generalized web site development. I don't call them frameworks, if for no other reason than not to confuse them with the lower-level frameworks like Zend.
Zend (CodeIgniter, Lithium, Symfony, etc.) are more general frameworks for creating virtually any type of web site, making no assumptions about how the web site will function, other than that HTTP requests will be received and processed, and then HTTP responses will be returned to the requester.
Which type of thing you use and which specific one of that type is dependent on what the project is, how well it fits one of the pre-fab apps like WordPress versus a lower-level framework like Zend, and how good your PHP and SQL skills are -- but there is definitely not a one-size-fits-all answer.
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
hi,arvgta,Strictly speaking, wordpress is not a framework.
I think there is no the best php framework, but best for your project.
And, you can view this site( PHP Frameworks ) to compare php frameworks and find a right php framework for your project. this site have a top 10 list,it is useful.