I have the common MVC situation in my PHP system: the Controller receive a request from the View containing $_POST data. Now I have th
'C' is best option. You should not let raw $POST data go in model as model is supposed to be generic handling store and load operations mainly.
Example : same model can be used web interface and Web services. On Web $_POST is valid but for web services its not. So model doesnt care how data is received but only how to store and load it.
Yii is definitely a clean implementation of MVC.