Hello.

these NIT's are good and it is just that these fall low in the table in terms of ranking. But believe when it comes to taking admission, the competition is too high for these NIT's as well.
Below are the closing ranks of some of the mentioned NIT's
National Institute of Technology, Arunachal Pradesh
Computer Science & Engineering- 11886 
National Institute Of Technology Silchar, Assam
Mechanical Engineering- 12876
National Institute of Technology Manipur
Computer Science & Engineering- 14462
NIT Sikkim: National Institute Of Technology Sikkim
Computer Science & Engineering- 14739
NIT Agartala
Electronics & Communication Engineering- 15304

I guess Manipur and Mizoram are equally good but check for the recent cutoff to choose the best of.

Hope this is helpful.

Good luck.