I am using using, Since 2009 and never felt to change or port to any other network.
Also I recommend my users to take prepaid plan not postpaid plans as when your postpaid net or minutes are ending they not inform you but in prepaid they do.Although it has good network coverage as I go many places and mostly 97% places the network works quite good.
Yes as services are so good its plans are costly and yes the speed of its 3G net is very good and I must tell you that if you have a dual sim then buy another sim for net of different operator as in Airtel 3G net gets over very fast whether you have 1 GB or 2GB. So for calling and good services Airtel is pretty good . So if you want to buy new sim you can use this.
Thank you!