I had been a customer of flipkart from a while now and have been ordering a lot of stuff from them they have a good customer service and mainly the tracking system is accurate.
And I can sometimes schedule the delivery as most of the time the delivery boy has asked me for time he can deliver to my place over all best results and good customer care support.
Main thing to notice with flipkart is the website and mobile app both are very responsive and supports both ios and android well you can also locate the seller and decide to buy the product or not checking if the delivery will be in time or not.