Hello Abhishek

BITS Pilani has a much higher ratio of people who have qualified IIT-JEE and moreover it has no reservations. So the students you can expect to meet in Pilani are going to be much brighter.
2. BITS Pilani has better management and very student friendly policies. For e.g. arranging for a bonafide certificate from the college just needs you to go and click on a link on a website, and the required document is delivered to the hostel room. In Mesra you need to 'go write an application' and stand in a line outside the Dean's office during a specific time in the day. Mesra is mostly student unfriendly, to put it lightly.