If  your branch is good enuf  to fetch you good branch at the old IITs. Then you shud opt for old IIT's ...

Considering the placements of old IIT's and new ones then  new IITs are not well establised, it is not a good option to pursue. New IITs dont have a very established placement cell or enterprenuer cell which looks after the welfare of the students, also they wont be able to organise various events which helps in personality development of the students.

Currently,IIT Kanpur is the best IIT.You should prefer acore branch in new IIT as they have better facilities and open other avenues.