First off all, you would be lucky if you get into any of the above. There are lakhs of people competing for places in this college. You have to work your ass off for something like your hypothetical question to happen in real.
Second, BITS is mostly renowned for CSE. Go for BITS if you want to do CSE else go for IIT Roorkee.
In the end, both colleges are excellent but both have their special branch for which they are famous for.