The answer to this cannot be direct,it depends on you.
What I meant by that is both the college are good ,but if you financially sound and are ready to spend around 20 lakhs for your college( 4 year fees of bits pilani) then you should choose BITS Pilani CSE
But if you are unable to spend or if it is difficult to spend 20 lakhs then it is advisable to go for IIT Patna .
Though both college are good and if neglecting the financial aspect by looking at current scenario you can opt for any of the two colleges , you are not gonna regret your decision.