These NITs are not lower ranked. Although these are located in remote locations, they have good infrastructural facilities and research interfaces. So, branding them as ‘lower NIT’ is not justified. 

I have a friend at NIT Silchar and according to him the CSE department at the institute is great. Here’s a glimpse of the recent placement statistics of NIT Silchar.

• NIT Hamirpur is also another great alternative, if you are getting admission at the institute go for it. NIT Agartala should be the next in the preference order. 
• Choosing VIT over these NITs may not be wise. VIT is not as reputed as NITs and there are rumors that placements at VIT are paid sometimes and students who get placed through campus placement get fired after only a few months. 
• Comparably NITs are less strict and you will have much freedom on campus. NITs are also better in terms of placements and extracurriculars. You will get to organize events, take initiative about things. Internet connectivity on campus at NITs is much better than VIT. 

If you can’t get into any of the three NITs mentioned above, go for NIT Sikkim. It is a great option, in case you want to go for higher studies like MS or MBA. In selection interviews, you will be given more preference over students from private colleges because of the NIT tag. But if you want a job after graduation, then VIT will be better as compared to NIT Sikkim as not many companies visit the campus because of its remote location.