Airtel, being the oldest company who is providing calling / internet / roaming and other type of facilities to its customers. Their network is very good even in the remote areas as I tasted in the area of Joshimath / Badrinath. Their network is OK even when the metro is going underground. Their customer services attitude is better than others. But I have to inform that their charges are subsequently high as compared to other companies. They are charging Rs. 100/- late payment of just going late by one day. In the current scenario their rates should be minimized as compared to other service providers.