[eluser]Michael Ekoka[/eluser]
I use and love both. If you're only getting your feet wet, I'd recommend to start with CI to get acquainted with the overall concepts. As you get more and more comfortable with architecture, have a look at what Zend has to offer.
Both frameworks have their own interpretation of the MVC pattern. There are some similitudes and some differences.
As a framework, CI can be classified as in between glue and full-stack. Meaning that some functionalities of the framework can be easily adapted to use external libraries, while others need a lot more tweaking. Also, not all native libraries can easily be pulled and used as stand alone components in non CI projects, because they assume knowledge and presence of other core functionalities. CI's architecture is quite "liberal". You need to only understand stuff like Routing, Controller, Models and View. That's it. Concepts like bootstrap files and dispatch are all handled by the framework. It is a very good choice as a first framework.
Zend on the other hand is a true glue framework with a minimalist core (front controller, request, router, dispatch, response). All parts of the framework are interchangeable/adaptable (even the core, provided you implement the key accessors to these classes). Think of it as a collection of libraries for people who want to build their own framework or feel the need to further customize the behavior of any given part.
You'll find that Zend is a lot stricter about architecture than CI (while remaining flexible). It shows in their implementation and in the documentation. Components tend to be described using specific pattern names (observer, registry, singleton, front controller, etc). It probably is safe to say that a certain familiarity with patterns is assumed. Nonetheless, a beginner can quickly grasp these concepts without paying too much attention to names.
Both documentations are excellent. A beginner will prefer CI's while a more seasoned developer will probably favor Zend's.
As a developer, you will pick up a lot of new concepts initially by going with CI, it will lay the ground work for more advanced topics later on. Its approach to solve certain recurrent problems encountered during development is quite clever and elegant and could be, for a programmer, lessons to be carried to future projects. As for Zend, it will bring you to yet another level. The architecture and the code is just that mature and convincing. Also, the fact that Zend was designed for PHP5 allows it to take advantage of some cool functionalities (the perks of evolution). You will discover a lot of things that you didn't know php was capable of.
