I have been Airtel pre paid connection since last seven years(since 2003). The journey has been a mixture of advantages as well as disadvantages. I have also used Vodafone(when it was hutch - in 2007) and Reliance CDMA(2007-2009).
So keeping all such experience in mind, let us review airtel on different parameters on a scale of 0-10:
Basic Service: Basic need for a mobile conection is to make/receive calls and send SMS i.e. connectivity whether in town or out of town. I would give airtel 9/10 on this.
Value Added Services: These services include hello tunes service, GPRS, Airtel live, Friend Chat, Astro, and many other services. I have used the following:
Hello Tunes: 9/10(Renewal and changing song charges you heavily when you choose a song)
GPRS:10/10 Connectivity is quite good
Airtel Live: 9/10(Speed is good but costs high on data download)
Customer Care: I have tried customer care by calling 123, 121, 12132(Technical Expertise) and 9810198101. Overall experience has been fair- 7/10. Sometimes customer care has been not reachable or non responsive but they have been very supportive.
Cost of services: As far as affordability of services is concerned, I would again rate airtel 7/10 as over all charges are slightly higher than other players in telecom sector.
That was all I had to say. Over-all Airtel is one of the best with great network and roaming(appreciable service). All Airtel needs is competitive rates for services clubbed with innovation.