Amrita has the best and largest campus amongst these colleges. The table shows a brief overview of the institutions.

Academics: (Winning Institution - Amrita University)

• The syllabus and especially the question paper is not the traditional type but rather stimulates you to think. 
• They have a much advanced, updated curriculum and it is possible because they don’t come under any university and hence have the liberty to mold according to the latest industry standards.

Placement: (Winning Institution - Amrita University)

• It is not easier to get placed from Amrita because you study in Amrita does not mean you will get high placements because the crowd in Amrita is more competitive. 
• All those who missed out on JEE come to Amrita. Top companies like Microsoft, Facebook, CISCO recruit only from Amrita out of those mentioned.

Campus Life: (Winning Institution - Amrita University)

• The clubs in Amrita are almost international, as it conducts the prestigious ICPC (International Collegiate Programming Contest). Which itself is a benchmark to look for, acknowledging non-premier institutes like IITs, NITs, and BITs. 
• The clubs in Amrita are more diverse and active. It's tech-fest ANOKHA is also much better. 

If you don’t have a blend with a very diverse crowd go for Amrita. Going by all the factors mentioned above, it is safe to say that Amrita University is a better alternative.