I had used my unlimited Airtel connection for almost 2 years and I am very much satisfied with it.
Sad I have to change my place and they are not providing connection to that area in Mumbai.
But I would recommend to buy Airtel over other ISPs. Fairly good quality net they are providing.
When I sent request to closed my connection, they immediately close my online account and I had to go to airtel store to pay my remaining amount.