Thanks for the Response. I could get little clue from your answer.

I hope If Allen or Akash or any other Book is referred they will cover NCERT as well as some add on. So will it be better than sticking to only NCERT.

According to me ncert is the best policy. Going through every word of ncert is what exactly you have to do. Going through also includes the understanding of each sentence thoroughly. At the end practice some test papers to test your self. Still if you have time you can have some additional informations too which is not must. According to previous year,most of the questions were the mixed concepts of 11th and 12th class and too purely from ncert. The only thing is you need to be very through with the ncert in both the years. 

Good luck.                                                Hope this helped you!