Depends on where you are. In Kolkata, Airtel has comparatively good service to the best of my understanding and great reliability. Although, their meter reportedly runs like a standard desi yellow cab. Dunno why TRAI doesn't take them to task over that. Oh wait, Sunil Mittal can get away with murder.
I don't have any idea about GTPL (GTPL-KCBPL in Kolkata), but if you want to experiment with cable broadband, GTPL's group company, Hathway, has the most attractive plans here by far (at least on paper).