Which is better for CS, IIIT Allahabad vs NIT Trichy?

Both IIIT Allahabad and NIT Trichy are excellent institutes imparting engineering education. Choosing the better between the two will require comparison based on some common aspects

• Campus life: IIIT Allahabad has a very rigid and restricting campus life as you will be surrounded by nerds. The academics are very tough and most of the time will be spent in completing assignments. NIT Trichy has a bit of flexible and lively campus life.
• Clubs: IIIT Allahabad does not look beyond academics and the extracurricular culture here is very lacking. The clubs here are very few in number in comparison to NIT Trichy which has more than 50 clubs.
• Coding culture: IIIT Allahabad being the academic m-oriented institute obviously has better coding culture than NIT Trichy which focuses on the overall development of its students. NIT Trichy has more students in core branches than CS. 
• Higher studies: If you are planning to go for higher studies such as an MS from a top foreign university, then IIIT Allahabad will be a better choice for you.

Considering the fact that the placement scenario of both the institutes is at par with each other, choosing one over the other depends on the kind of college life you prefer. If your goal is to just study and get placed in a top tech company, then IIIT Allahabad is a great choice for you but if you want to experience a good campus life and enjoy your engineering years, then NIT Trichy is better.