Chandni chowk- best place to have street food at the cheapest prices and you will also be able to find a variety of sweets such as shahi tukda to balance your taste buds after a chatpata experience.
So it's depend, if you like to have butter chicken and biryani go to Moti Mahal, Daryaganj
New Minar, GK 1
and for the best veg malai chaap and similar just go to Veer ji Malai chaap, Geeta colony
In fact the whole Delhi area is good but than it also depends whether u want budgeted food or regular. Old Delhi is the best especially Chandi Chowk area.
Street food the word makes us starving and feel like mouth watering. Delhi is one of the most famous city for street food. Where the food lover gather and enjoy the street food every day.
Here I have gathered some street food places to you:
Chandni Chowk , Majnu Ka Tila ,CR Park, Rajouri Garden, Connaught Place.
Famous dishes of Delhi: https://www.indianeagle.com/traveldiary/famous-dishes-you-must-try-in-delhi/