IMO the most important decision you have to make is if you want a glue or a full-stack framework. A glue framework like Zend provides you with components which you can use either way you want and does not restrict you to use any of them. A full-stack like CodeIgniter (and Yii?) does the opposite, it restricts you to it's feature-set but it requires less effort on your end to write the application as bootstrapping and resource loading is all done for you (it runs out-of-the-box).
I don't think there is much else I can add to this to be more relevant to you, download a few frameworks of which you think you like and try them, create something small, amuse the masses

[ot]PS: Developers of the modern age get no respect. We are always the blunt of jokes, the first to blame, and people hardly talk to us. I wouldn't trade it for the world. -- love it

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