Previously I was subscriber of Vodafone but due to un-satisfactory service, I had to switch to Airtel.
Once I am with Airtel, I never got disconnected. Always mobile network is on specially if you are in any metro city like Delhi/Mumbai/Chennai/Bangalore. If you are in some small city, even if Airtel service is not as good as in Delhi but still better than other Mobile company like Vodafon or Idea.