Initially I had Airtel during 2004, then changed to Spice ( Idea Now) since there was no free SMS offer on Airtel then. Had the spice Sim for almost 5 years till 2009 Oct, but then suddenly while a recharge my plan got shifted so had to change the sim back to airtel! Now I am using Airtel without any problems. But I agree the CC of airtel is sick, they take complaints, and will tell a particular date on which their officer will call us back but till date no one called me! Apart from CC there's no problem with airtel.
I also like airtel because of the mChek service which is helpful in recharging my sim any time any place without going to the recharge outlet, without even GPRS and any additional charges. All you need to have is a credit/debit card or bank account which you need to link to your sim. Create a mChek pin and get going!! You can even recharge other airtel numbers prepaid or postpaid!