Which is better: CS from KIIT or mechanical from Thapar University?

Having known some people studying in both these institutions, I can say that KIIT is promising and is getting better every year. Thapar is a well-known and much older institute. You can choose either by preferring the college or the branch.

• If you are interested in studying mechanical engineering then go to Thapar. It has good placements for Mechanical. The faculty department is also decent.
• If you are more inclined towards coding go for CSE from KIIT. It is a more practical-oriented subject.
• If the interests do not lie in either and you just want a B.Tech degree and want to pursue higher studies or MBA, then go for CSE as that is the easiest among all the others. 
• It will be more practical-based learning, more industry-oriented and it has the best scope after graduation.

So you should decide your field of interest and what type of job or higher studies you would like to do and then opt for the branch that fits best for you.