Should I practice the GregMat questions or the Manhattan 5lb book or the Big Book ?
I have around 1 month of time left
I would recommend the GregMat questions. There are clear flashcards and lessons for each topic, and they are designed to simulate the real test.
However, if you run out of GregMat questions or feel that you would like to test it out, feel free to try the Big Book or Manhattan 5 lb book.