I am using airtel sim card from last two year and the network coverage is very good in my area.
The speed of its 3g network internet is very good.
I didnt try the 4g network of airtel yet but I am very much satisfied with the airtel sevice.the customer service is also good.yeah its tariff and data plans are little costier than the other sim cards but you feel free when you get the convienent service . My father and my brother is also using airtel.i do have a docomo simcard but when I travel in roming it doesnot allow data connection but in airtel sim there is no suchbtypes of problems.this ia very good open network . I just loved the service.