Hi Kishore
Biotech has not been a very attractive department specially with regard to jobs. It has a lot of scope abroad if you procedd to do a PhD though. So please opt for it only if you only want to enter research in future.
In general, weigh your choices this way: Mechanical>Chemical>Aerospace>Industrial Engineering>Ocean engineering and Navarch> Metallurgy>Mining in which ever IIT according to your availability. I think going to any of the old IIT's [which include Guwahati and rourkie] is a safe bet with regard to jobs and research opportunities in future. If you are keen on opting a better branch, maybe you should try Guwahati and Rourkie.
Also, a couple of M.Sc courses like Maths and computing and economics have registered excellent placements this year, even better than some of the BTech courses. You could maybe place these departments above OENA if you do not mind an MSc degree. Though, these courses are available only in Kanpur and Kharagpur.
Regards
KishanS Srinivas
Askiitians Expert