There is lots of mall in Delhi you can enjoy every where in Delhi. its hard to say which mall is best and which is not because there is mall according to your budget. there is mall that is costly and low prices shop both.
If you will try to find the reason for best mall than I think you cant do this. because there is lots of mall and all mall are fill with peoples. week days all malls are empty and week end all malls are full on peoples.
Evrey one chosse the mall of near their home so I don’t think there is any reason to find the best mall. Because price are according to showroom and brand.