My son got 200 marks in Mains and 971 marks in AP Inter Board Exams. Expected Mains Rank as per 2014 is 6500 to 7000. My question is whether to opt for IMTECH in IIIT-Bangalore or Mech/Civilin topNITS(as there is no chance to get CSE/ECE in NIT s of South India)Please suggest.

As of now I think the prime focus should be JEE advanced exams. I think with his marks he should get through advanced as well and get a good IIT.
As per your question , I think Mechanical and other core-branches in NIT’s is a better option than IIIT-Bangalore. However going into modern norms , just doing B.Tech and B.E won’t sufice , pursuing higher studies is a must. Kindly plan accordingly.
Also CSE in any NIT is a better option than core braches. It’s a modern day ever-green field which never goes out of future prospects,