I have friends at both IIIT Guwahati and LNMIIT and based on what I heard from them, I will recommend that you choose LNMIIT. Here are the reasons why.

• The campus life over there at LNMIIT was far better than any other college. In case you are someone from the North, you'll have difficulties adjusting to Guwahati. There isn't anything to find here be it a good social life, or cafes to chill at.
• In terms of placements, LNMIIT has so much to offer. 
• In recent years it has made tremendous strides, some even claim that it has become better than Thapar University.

Being said that you can go to IIIT Guwahati if the course fee is a matter of concern for you. It is better than taking student loans for LNMIIT. IIIT Guwahati is also a viable option.