you should purchase from above four. I had bought 4 test series and daily I used to attempt 2 mocks daily. By the time I reached my preliminary exam, I was confident enough that I knew I was prepared. And that feeling alone is more than enough to get you through the exam.
[/size]Coming terms of notes or videos, I preferred YouTube. There are many channels which you can prefer. I have heard some positive reviews about WifiStudy, Adda247, and Gradeup. My personal favorite was Meritshine. This must be new for you so go ahead and check[/color]