Hey

NISER is National Institute of science education and research and NIT is  National Institute of Technology as both the institutes are best at there place but if you have taken admission in NISER then go for it only beacuse it is good for Physics and faculties here are good enough and also the placement at NISER is available at a large variety if you have CGPA greater then 7.5.  and also you will get  two year to complete your Msc project in physics which is quite good . so, stay with NISER dont get confused , i hope it will help .

Good luck