Software Tester is as such No Branch in IITs, But a computer science Engineer does the same Job so To get into IIT, Nit You can Follow the Opening closing rank by JoSAA to find the required rank in the relevant category for You here:

https://josaa.nic.in/josaaorcrarchieve/Result/OpeningClosingRankArchieveN.aspx?Year=2017

Among IITs and NITs, there is No doubt that IITs are better compared to NITs in terms of Research Works, Campus Life funds Received By Governments and as well as students.