IIT Patna.
Both IIT Patna and IIT Ropar are 2008 established IITs and both are improving at a rapid pace. There’s not much to differ between the two institutions but if asked exclusively about Cse department ,IIT Patna and Indore are much better than their 2008 counterparts (barring IIT Hyderabad, which wins owing to its industrial location.dont know much about its cse).
If you look at the achievements or activities –
1)IIT Patna qualified multiple times for ACM ICPC(regarded as olympics of coding) world finals (the only 2008 IIT to do so except IIT Indore).
It shows the class of coding culture. It is comparable to the old IITs also.
2)IIT Patna had 14 Gsoc selections last year,which is the highest amongst 2008 IITs, Infact more than some old IITs also. This year also, IIT P had many. In fact, first yearites here get selected In Gsoc.
3)DSC(a club sponsored by google for developers) and codechef chapter has even strengthened things .
4)Apart from acads and coding ,the extra curricular clubs are quite active here (although I think it’s same in Ropar).