It's difficult for me to say whether choosing IIT Guwahati CSE over IIT Varanasi CSE was a mistake without more information about your specific circumstances and goals. Both IIT Guwahati and IIT Varanasi are highly respected institutions, and both offer strong Computer Science programs that are rightly comparable in almost every aspect.

The placement scenario is similarly decent at both institutes with very little emphasis on research. The active Coding Club/ CSEA at IIT Guwahati gives it a slight edge over others. Both the institutes are excellent choices for whatever you want to do after graduation be it research, open source development, or a stable job.

The only distinguishing feature is the weather as IIT Guwahati has better weather conditions than IIT BHU. However, this flaw is compensated by better connectivity of Varanasi being on the mainland. 

Both IIT BHU CSE and IIT Guwahati MnC are excellent options and the choice of the branch is a personal matter depending on the candidate's preferences rather than the credibility of the branch. Here are a few parameters on which we can draw a general comparison between the two courses.

• Course structure: IIT Guwahati’s MnC program has a well-structured curriculum with the perfect blend of Computer Science, finance, and Mathematics courses. By the end of the program, you will be eligible to sit for software as well as finance placements. IIT BHU CSE too is known for its flexible course structure with a plethora of electives to choose from.
• Coding culture: Undoubtedly, IITBHU has a better coding culture than IIT Guwahati. The ambiance is quite competitive at BHU if that’s what you are after. However, MnC too is gaining popularity and the decreasing opening rank can be seen as a proof of the same. 
• Peer group: High JEE rankers prefer IIT Guwahati over IIT BHU and thus the peer group of IIT Guwahati is more refined and superior in quality. 
• Campus and student life: IIT Guwahati has an amazing campus and its students get to live a very dynamic and lively college life. IIT-BHU’s campus on the other hand is underdeveloped and you can also find student politics here. IIT Guwahati is the best choice for nature lovers who like solace and peace while IIT BHU is for those who want to experience city life as well. 
• Student life: Both institutes have great clubs and activities to promote the holistic development of students. Students are allotted single rooms right from the first year at IIT Guwahati which is different from IIT BHU. Mess food is better at BHU. IIT Guwahati is a clear winner in sports, cultural and technical clubs, etc.
• Placements: Both institutes have equally good placement scenarios with major recruiters like Microsoft, Google, Tower Research, Flipkart, etc. visiting both these campuses. CS and MnC students receive similar placement offers and in fact, being in MnC makes you eligible for both finance as well as software jobs. 

Both the institutes and branches have their own strengths and weaknesses and the final decision should be based on what you want from your degree. If it’s a competitive environment you are after, go for IIT BHU, while if it’s a rich college life experience you want, then IIT Guwahati is your destination.

The choice of the institute between IIT Gandhinagar CSE  and IIT Guwahati ECE depends if you want to follow the branch of your interest or want just go for the brand name of the institute. 

If you value a branch more than a brand then go for the institute that offers the branch of your choice. If you are inclined towards CSE, then go for IIT Gandhinagar without much hesitation. Despite being a new IIT, it offers the IT tag and education at par with most IITs. Don’t let the fact that it’s a new IIT demotivate you. The students maketh the college and not vice versa.

But if you are bothered by the brand value and are hesitant about joining a new IIT, then go for IIT Guwahati.

I am assuming that you are asking this question after the first round of seat allocations are announced. If you are confused between IIT Gandhinagar CSE and IIT Guwahati ECE, consider the following points:

• People may tell you that you can do coding along with ECE, but the reality is far from true. CSE is much more than coding. Its curriculum revolves around mathematical concepts like linear algebra, statistics, probability, logic, differential equations, etc.
• Institute-wise, both options are equally good with IIT Gandhinagar having a slight advantage because of its early establishment. But the opening ranks are similar so both the colleges attract a similar crowd.
• It’s a no-brainer that CSE offers better job opportunities than ECE. Currently, everything is about data sciences and artificial intelligence which has witnessed an increased demand for well-trained CSE engineers. Although CSE engineers from every college receive high pay, your IIT tag adds to the value. 

Both the colleges will provide a good learning environment and ample opportunities so go for the one that aligns with your interests the most.

B.Des (Bachelor of Design) programs at IIT Bombay and IIT Guwahati are both undergraduate programs that focus on design education. However, there may be some differences in terms of the specific curriculum, perspectives, experience, and course offerings at each institution.

• Experience: IIT Guwahati B.Des is known for its excellent experience in handling undergraduate students. The course is older than 2 decades and has been through constant revisions to make it industry relevant. IDC, IIT Bombay is also one of the best design schools in India for technical design, M.Des that provides great exposure to its students.
• Perspective: While IIT Guwahati strongly focuses on science as an important part of design, IIT Bombay does not. It solely focuses on design with little importance to technical stuff. 
• Faculty: The faculty pool of both institutes comprises extremely learned and experienced professors that are genuinely passionate about design and teach in such a way that students also fall in love with the course.

Ultimately, how much you gain from this course depends on you only as it all is about learning, observing, and experimenting. No one can help you in design, you have to explore everything on your own.

I am assuming you have no specific interests and are looking for a branch that offers good job opportunities. In that case, Maths and Computing at IIT Guwahati is best. With the unique blend of Mathematical concepts and CS concepts, this program has become one of the most coveted ones only second to CSE. Indeed, MnC has an immense workload and is considered difficult but so is ECE. However, if you are not interested in Maths at all, and are a research enthusiast, Electronics is better than MnC. Electronics will give you an opportunity to explore both IT and hardware industries. However, it’s very difficult to secure internships in CE than MnC and this might demotivate you a bit. 

Concludingly I would like to comment that MnC is a good option in the short run while ECE will prove to be beneficial in the long run.