Best would be Reliance CDMA prepaid and Airtel Corporate 249 plan in post paid in chennai. The worst would be BSNL.
Inside Office, house and shopping malls there is no voice clarity. You will have to run out to the street to get clear voice. Vodafone is best in terms of GPRS.
Vodafone service is also ok in terms of voice clarity. However, to select a network you will have to be clear as to what would be your prime look out in a mobile connection. Whether cheap call rates or GPRS or voice clarity or a mobile phone just for incoming calls.
For example Call rates are excellent in Reliance prepaid, if you go in for life time jaadu pack {Rs.550} all local calls {mobile to mobile and mobile to land land line within Tamilnadu including Chennai Circle} would be 50ps and all STD 1Re. Often there are excellent recharge offers. For example for Rs.555/- top up the talk value would be Rs.1100/-. In effect your local call rate would be 25p and STD 50p considering the increased talk time offered.
But there is no GPRS is Reliance phone. You will get only R-world. Vodafone offers excellent GPRS service, but the tariff is no good. In Airtel prepaid, the customer care service is worst, you can never talk to customer care person. Everthing would be in automated voice. But the customer care service in Airtel post paid is very good. If you are a person concerned being honoured by the service provider go for Airtel post paid.