See, if you are failing continously, there may be some fault in you and dont make a habit of changing books every time. Basically every book has the same content but what differs is the way they present their answers.
Please get a certified copy of your answer book, see where you are losing marks. Get good knwoledge over all concepts, make a habit of writing answers on your own and compare those answers with the PM answer. Then you willl get a clear idea of how to improve.
Institute books should be the first preference, if at all you require any other book, then its completely based on your choice to select right author.
Dont worry, follow the tips, surely you will pass....cheers