Among these three the best college will be AEC (Assam Engineering College) and here are some reasons to justify it. 

• AEC is completely an engineering college, but the other two are schools for engineering under their respective universities. AEC gets its funds from the state government and it is given solely for the purpose in the engineering field, but the other two institutes receive their funds from the central government and it gets divided among all the departments available in the university. 
• AEC is now a pioneer in the field of engineering as it has completed more than 60 years of its existence but the other two universities are very new in the field of engineering. It has also built a very strong alumni network within these 60 years of offering engineering courses. 
• As it is located in Guwahati, it has many advantages over NEHU and especially Assam University. It is located in Silchar and there are many connectivities and traveling problems due to which many companies don't visit the campus during placements. In 2020, placement drive it offered salary packages upto 10 LPA. 
• In AEC, the lab facilities available are very good and are much better in comparison to NEHU and Assam University. 
• In these 60 years of existence, AEC has established a very good reputation all over the country with its excellent academics and placements and most of the top scorers prefer to choose AEC over the other two to pursue their engineering. 

Hence, if you're interested in pursuing engineering, then choosing AEC will be a very good option as this college has a very good reputation and experience in this field and offers very good facilities and placements to its students.