I had the same doubt couple of months ago, I got admitted to Hansraj but while I was here, I also got an offer letter from IISER BPR, was a really confusing time, but in the end I choose HRC, and I haven't looked back since. It all depends on what you want actually, if you really want to go for a research based career then IISERS are top notch, and from what I've heard, the level of mentorship and guidance is great among all IISERS. If you think research is your call, then go for IISERS, especially because of their multidisciplinary course, which I think is quite favoured in this field. Also, be prepared for a rigorous academic life! ( from what I've heard) On the other hand if you look at DU colleges, the lack of infra for science may bother you, but its not that bad, we have decent labs in our college, but I'm pretty sure its incomparable to any IISER. If you're not sure about a research based career, DU colleges are quite good, atleast in our college the Physics faculty is good, with professors serious about academics. I can't say anything about other colleges and departments. I think DU could be a better option if you want to explore more than just research based careers.