This totally depends on your aptitude. If you are interested in Literature than you should go for it and if you find Linguistics interesting then you should apply for Linguistics. The difference is also of so-called 'Scope' of both degrees. Some say Linguistics has more scope than Literature. But what I have seen both are of equal importance as the prime concern and focus of both degrees is to join the Lecturer-ship/Professorship. More or less doing MPhil/PhD in Pakistan means you are paving way to be a part of University Faculty. Research trends in Pakistan are well known to all. So, basically after doing MPhil/PhD there are seldom any scholars who seem interested in doing True Research in their respective fields. It is pertinent to mention that MPhil is essentially a Research-Oriented degree, however, recently NUML has included too much stuff in course work. Nonetheless, you have to frame your mind with a researcher's perspective. It would be a totally different experience from Masters, I hope.

If you go through the previous posts of this thread you will get the answer to second part of your question i.e. Type of questions asked for Linguistics and Literature.

Hope this would help.

Regards