Hello.
As you will be familiar with that the admission for Btech in NIT is done on the basis of your JEE mains rank while in IIT it is done on the basis of your JEE advanced rank, while the admission in IIT for MTech is done on the basis of your GATE score, rank.
If we consider the difficulty level of JEE mains and GATE exam then it is found that the difficulty level of JEE mains is lesser than the GATE exam if we consider with the student level of education so same it is easier to qualify JEE mains in comparison of GATE  exam whitch designate that the chances of having admission in NIT for BTech are more than Mtech in IIT while if talking about the placement  so definitely you can have good placement in masters even from IIT also.
Best of luck.