Pls suggest, best book for idt

i am using Bangar... but only past exam ques are given in it....and it is in ques ans format.. can anyone tell is there any other book of Bangar where concepts are also given... other than bangar which book should i consider ???

either NS Govindan or VS Datey

thanks to all of u for valuable suggestions.

V.S DATEY is a book which is recommended by ICAI.....and with a good presentation and coverage...