IIT Delhi has both old as well as new hostels and obviously the new ones have better facilities and infrastructure. The new hostels are Girnar and Udaigiri and have spacious rooms and have 8 floors each with a total of 400 rooms in each hostel. These hostels have a big crowd which means a bigger hostel family to interact with during events. The mess facilities are also considerably better and bigger than old hostels.
The old hostel buildings have only 3-4 floors with smaller rooms and less facilities. But these hostels have a nostalgia associated with many toppers who are successful people today. This spirit keeps the ambiance of these old hostels lively.
Honestly, I wouldn’t say one hostel is better than the other. Every hostel has its unique aspects and cannot be compared.
As for the choice of hostels, no, you cannot choose your hostel. It is allotted to you randomly at the time of admission, every hostel having a mixed bag of students. You cannot change your hostel unless it’s a serious issue.