Airtel is one of the best mobile operator in India. using from last 2 years and did not faced any issue with signal. and also good customer service.
It has good network all over India using Postpaid connection is affordable and great CUG facility within our group for the price point the only issue with my plan is using 2G/3G. Data are not that affordable and some times 3g becomes 2g in my room so I need to go outside.