Long story short, if you are a beginner with MVC and want to learn a framework from the heart, start with Zend Framework or CakePHP. Soon you will realize that you may not have to move or use any other framework unless the situation requires it. Saying that, there are other very good frameworks out there like Yii, CodeIgniter and Kohana (started as a fork of CodeIgniter and later it became what it is now)
And again I am answering the title question “Which frameworks is best” – there is no such “best” thing to be honest. The one that suits your need is the best framework for you.