I bought Airtel 4G sim about 3 months ago and I am fully satisfied with the service provided by Airtel.
I bought Airtel because of large network coverage area( as people have been talking about - and is true) .
Airtel is a bit costlier than any other mobile operator like Vodafone, Reliance and Idea but its worth the money.
As far as my experience is considered I have faced no problem till now and I haven’t called the customer care a single time.
I bought the sim because I wanted to try 4G and wanted a good network coverage due to my travelling condition.