I have been using the airtel mobile service since few years.It is best in network coverage.
If u are in underground or, between buildings, you will have a network of at least single needle. They are providing 2G, 3G & 4G internet with lower internet charges.
Good internet speed in all areas.They have attractive call tariff plans and internet tariff plans.Another great advantage is their customer support quality, Service center executives will sort out all your problems within short time.