I used airtel since 2005, before that I used many network but I experienced airtel is the best. no doubt that Airtel costly then others but value for money, if you moving somewhere on highway/railway track and your mobile showing one point of signal level you can easily make call and use internet without any inconvenience in comparission of others. and one more thing that if you are going deep area in mid city where signal availabe in low frequency and someone trying to call you so he/she will easily make call on your cellphone.
Airtel gives services till end point of the signal frequency.
Thanks