After grappling with the beast that is the Zend Framework and others I eventually settled on Kohana because of its simplicity and speed. Kohana was originally a community developed branch of the popular CodeIgniter framework, but with the release of version 3 it has taken on a life of its own.
My previous framework experience has been with the two big Coldfusion frameworks Mach-II and ModelGlue; and while both of these frameworks are excellent at organizing large Coldfusion projects, the XML config file(s) in both frameworks have always been a pain point for me. It was great to work with a framework that doesn’t require endless tinkering with XML.
I’ve really enjoyed working with Kohana. It is unobtrusive in your code and provides a straightforward platform to build your application on. You can use as much or as little of the functionality it provides as you need. Its allowed me to focus on building the app logic and not creating low-level functionality.
If you are about to start building a new PHP app I recommend you give it a try.