VK Singhania is for indepth general study of Income Tax.
TN Manoharan is specifically for CA exams.
But, if you are giving exams in May 2015, then the time to study from VK Singhania and TN Manoharan is long gone. Both books have 1000+ pages. And you have other subjects also to cover.
You need a short and crisp study material.
Go for the latest Practice Manual + RTP for May 2015+MTP for May 2015.
This will suffice for IPCC exam.