My sister used to be a student of Thapar University so I think I can give you some information regarding the institute. 

Let’s take a look at the pros and cons of the TU.

Pros-

• The infrastructure is really good. You will get Wi-Fi at around 4Mbps, Sports facilities are good, and the accommodation is really good.
• There are a lot of research opportunities that you can pursue without a lot of questions.
• You will have to attend college only 5 days a week. You get off for 2 days and you can travel around a city.
• Patiala is a nice city. It has all the basic amenities.
• There are a lot of cultural events and societies you can be a part of. The campus is really good.
• The placements are really good. According to the recent statistics, the highest package offered was 28.5 LPA.

Cons-

• There are teachers who are fresher in the field of teaching and lack the skills required. 
• There are a lot of cultural activities, but the students raise the money only by the exterior motive of making money.
• There are societies like Student Alumni Interaction Cell (SAIC), with biased selection criteria. 
• There is the 75% attendance criterion.
• There is a 50% Punjab quota. You might see people with half your JEE marks in the same branch as you are.

Apart from this, the placement report of the college is good. Just keep your pace and give your best in your studies.

MDU Rohtak is an average university. Although there are not many opportunities made available to the students you can turn the tables with your caliber and skills. 

If you are a mediocre student with good writing skills then MDU would be the best fit for you. The students tend to write gibberish in the examination halls and yet pass their exams in the first attempt. Assuming that you are an average student, scoring good marks in your exams would not be much of a challenge.

If you are pursuing the course only for procuring a degree then UIET MDU would be a good decision. Your college life here would be quite challenging as you would have to fight for the bare minimum. For lab keys, placement opportunities, better grades and such are a part of this fight.

Otherwise, your passion for the course would be well catered at MDU Rohtak. Make a decision you do not regret later.

No, the administration is not particularly the best at Sikkim Manipal University. I know a few people from the institute and here is what they had to say about the institute. 

• There is a huge locational disadvantage of the university, given the constant issues faced by students. Recently, they have installed an ATM machine.
• The mess of the institute is not in its best condition. It is run by local people. They do not especially get concerned about the complaints students usually submit. The quality of food is not good even though they take exorbitant amounts of money for the food.
• The administration doesn’t take the necessary steps to resolve the issues raised by students.
• According to one of my friends from the CSE department they were not allowed to take industrial training from other companies.
• The professors are not gonna invest much of their time in your project. However, your project may get rejected for silly mistakes.
• Recently, in terms of placement, TCS rejected SMIT, while Amazon only hired students as their interns. The placement scenario is not good. 

This is everything that you should be aware of before enlisting at Sikkim Manipal University. 

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.