which book is best Pakistan Affairs by Ikram Rabbani OR Pakistan a hard Country by Anatol Lieven?

Both books can be used.

However, Pakistan-a hard country talks of why Pakistan IS the way IT IS.

It seeks to specifically answer this question. So, in order to understand Pakistan's dynamics, the book is a great read and may help you in your analysis and developing a viewpoint. As regards to syllabus, ofcourse it is not a coursebook, nor was it written in that light. So, I will recommend a reading of that book but not to solely rely on it.

As far as Ikram Rabbani is concerned, the book gives you material to gather from; so does Nigel Kelly, Farooq Bajwa and others.

A trek to Pakistan is also another good resource.

SO, read from multiple sources, to develop a comprehensive view instead of relying on a single source. Again, this does not mean reading everything and anything in all of these books. you may have to pick and choose of what to read and what to leave.