I'm not fond of any of them. Zend Framework, for example, is merely a big list of packages. You might as well just slap stuff together from PEAR. Hell, it doesn't even have a method for loading models when building an app with modules, yet they support flickr natively? Go figure.
Regarding CakePHP. It's not to bad, but they try to mimic RubyOnRails to much, which you just can't do in php without crazy hacks. This leads to slow execution time, which was mentioned.
CI isn't to bad, but I dislike the "keeping backwards compatible with PHP4" crap.
