One of my friends was in the same situation at the time of his counseling. He had this doubt and I am sure many of the people would have it too. I will note down the pros and cons of these two colleges so you can take an unambiguous decision.

IIIT Allahabad:

Pros:

• IIIT Allahabad has a huge campus and it’s beautiful over there. In terms of campus, IIIT Allahabad is definitely better than MNNIT Allahabad. 
• IIIT Allahabad is known for its coding culture.
• You will not be taught anything unnecessary like teaching engineering drawing to a CS student.

Cons:

• The faculty base is not that great. Sometimes even seniors take the classes. 
• The timetable along with the assignments becomes very hectic at times.
• It is also a new institute. 

MNNIT:

Pros:

• MNNIT is a very old college and has a rich alumni base.
• The placements are amazing if you are persistent with your hard work and studies.
• The faculties are good apart from a few. 

Cons:

• The campus is small as compared to IIIT Allahabad also; the sports facilities are also just not that good.
• If you are looking for a good coding culture then it's here too but far less than IIIT Allahabad.
• You will need to study some subjects no matter which branch you belong to in the first year.

The table below gives a brief overview of the two institutes.

So this pretty much sums up these colleges. The final decision is yours, compare and choose wisely. 

The most practical thing to do here would be to begin with taking a look at the syllabus of both these mentioned programs. You need to be absolutely clear about whether you wish to study for the next 4 years of your life and maybe also be able to develop a career in the same field. Interest and passion are mandatory to be able to sustain in any field of engineering for a very long period of time.

Now as far as my personal opinion goes, since two of my brothers have completed their engineering from IIIT Allahabad, I strongly believe that IIITA is a notch better than the others. Although the syllabus of CSE and IT is more or less the same, the overall academic environment of IIITA is better suited for coding when compared to the other NITs. There are a number of competitive programming websites available online where you will find more students of IIIT A placed at higher ranks than NITs.

There is a process of development, evolvement and growth as a programmer in IIITA for the students. It is known to all that India’s best coder Suryanarayana is also from IIIT A. Another reason why IIITA is a popular option for many aspiring coders is because unlike other colleges, it offers core subjects from the first years itself.

The placement scenario is also far accomplished of IIIT Allahabad.

One of my friends is a student of IIIT Delhi and he has visited IIIT Allahabad on a few occasions. Here is his insight about both the institute. 

IIIT Allahabad: 

IIIT Allahabad has witnessed a severe leadership change in the last few years. It had difficulties in retaining their faculties. A lot of students complaining about the previous Director, lack of faculty, hostels. The new Director is working to improve things, but it will require time. 

There were a lot of negative stories about the place in the media in the past, but none of them seemed to have made an impact on admission. students recruitment. The institute has always attracted top JEE rankers.

IIIT Delhi:

On the other hand, IIIT Delhi has not only attracted top faculty but ensured their retention. The environment on campus is quite good. Both students and faculty seemed to be happier compared to IIIT Allahabad. 

The table shows a brief overview of the institutions.

Overall, IIIT Delhi offers a much pleasant campus experience as compared to IIIT Allahabad. However, despite the negative publicity, IIIT Allahabad is quite reputed and attracts top JEE rankers, so, will have a great peer group. And if you genuinely want to learn, you can do that from IIIT Allahabad. 

This is a really nice question to ask. IITs only focus on developing good engineers, it does not focus on the mindset of people.

For a moment, let us forget about the packages and only focus on popularity. The popularity of an institute depends on how old it is because this impacts the alumni network, its history, and oral communication which contributes to publicity. 

• When asked for advice, many people talk about IITs and NITs because they have been functioning for so many years now and more importantly, were at their best.
• If you ask a current engineering student for advice, you will get better suggestions. There are 25 IIITs in India and not all are famous. But, IIIT Allahabad and IIIT Hyderabad are at their best and par with IITs in terms of academic standards.
• Factors such as academic curriculum, infrastructure, faculty, culture, placements, etc, should be the factors to be considered rather than how many might have heard of it or how popular the institution is.
• The course curriculum is something that IIIT Allahabad should proudly brag of. 
• It offers a great coding environment and is way better than MNNIT Allahabad. Also, IIIT Allahabad is ranked number in SPOJ Rankings.

In the coming years, IIIT Allahabad will surely be among the top popular institutions in India. IIITS are central government-funded institutes that specialize in Information Technology, which the IITs do not provide.

Harsha Suryanarayana, one of India’s first Red Coders, was from IIIT Allahabad and every IT person must have heard of him. He also represented IIIT Allahabad in the ACM ICPC World Finals. When it comes to regional rounds, many teams from the institutions win in comparison to teams one or two teams from MNNIT.

Talking about rankings and placements, IIIT Allahabad is above about 25 NITs and many new IITs.

One thing which attracts students to IIIT Allahabad is their convincing placement record. The main reason for this is the strong coding culture they follow. Students have an unconditional love for coding here. The time spent at IIIT-A will be pleasant as it's not just about academics but there are other fun activities on campus. You will get to be part of various tech clubs which will improve your practical approach towards your field of interest. Music, sports or literary clubs will give you a good opportunity to widen your network. 

Campus and infrastructure:

• The infrastructure is excellent which includes well stocked libraries, well equipped labs and 24×7 computer center. 
• You can also choose to hang out at the sports facility, shopping complex or Student activity center (SAC), swimming pool, gymnasium, cricket/football stadium inside the campus.
• The well maintained hostels provide 24 hour electricity and high speed internet.
• It has better mess facilities than any other engineering college.

To sum up, IIIT Allahabad has it all. It gives you a perfect ambiance to study and reach the sky. It gives you wings to fly and is a great place to enjoy. You will get to make a lot of friends and create the best memories of your life. If you get a hang of balancing your academics and social life, your campus life will definitely be incredible.

My brother is currently studying IT at IIIT Allahabad and according to his first-hand experience and your interest in IT, the order of preference for you should be:

IIITA>MNNIT>BITM>MANIT

It is because if you are genuinely interested in IT then IIIT Allahabad is the best option you can choose because of the following key points:

• The campus is well equipped in terms of infrastructure and facilities and the coding culture is quite good there. Also, it is an institute specifically made for IT, so the infrastructure is planned according to it.
• The course structure at IIIT Allahabad is also strikingly different from what you'll find at any other engineering college in India. It focuses a lot on programming and electronics-related subjects, right from the first year itself.

In NITs, you need to study a lot of subjects not at all related to your branch or course!

However, MNNIT or BIT Mesra may prove to be better options in case you realize that computers are not your cup of tea and decide to go into the non-tech sector. You will have a lot of diverse companies visiting these campuses, while in IIIT Allahabad you’ll see only IT companies coming to recruit.

Also, JEE Main rank of all the options you mentioned will differ from each other. So your rank also plays a major role in selection.

A few of my friends are alumni from IIIT Allahabad. The scope of the Dual Degree BTech + MTech course is good.

• For the first 3 years of the course, the curriculum is exactly the same. All the students (Dual Degree as well as BTech) attend the same classes, sit for the same exams, get the same results together. However, from the fourth year onwards, the specialization courses start.

• Once you complete the dual degree course, you will be eligible to sit for the same placement rounds as BTech guys. The results of which depend entirely on your knowledge & skills you have acquired during last 4-5 years.

• However, Dual Degrees will especially help you if you are interested in R&D areas.

The only reason that the cutoff is a little bit lower for Dual Degree courses is that many of you might be hesitant to spend one extra year in college. But for a college like IIIT Allahabad, it is worth spending an extra year. Sadly, in 2018 the 5-year dual degree courses were disbanded due to some administrative instability.