You should choose Zakir hussian Delhi college for BSc (hons) Mathematics as it has very clean and well equipped laboratory for math department and various college societies . ZHDC also is a very old college with very good reputation the surroundings(area around zhdc is very good you will be around some very famous places for hanging out with your friends) and it has better  ranking than Deshbandhu college. ZHDC also has very good crowd  and infrastructure.

There is not much difference between both the colleges both are offcampus colleges, fees are almost same  but the infrastructure of deshbandhu is not that good whereas the new building of Zakir hussain delhi college is spectacular. Before choosing college you should also look for distance from your house.

Hope it helps.