I have recently started banking with HDFC(3 months) and my experience till now has been quite decent. The ATM service is quite bad.The most common ATMs you see around you are ICICI and branches of State bank. In case you do manage to locate an HDFC ATM, chances are it won’t be in a working condition! Well, that has been the case with me atleast.
The internet banking services are quite good.you can use it for a lot of transactions online.and I have conveniently used it quite a lot. Once, I did use it to make a movie booking and the money got cut without the booking being made but the money was refunded within 3-4 days. I had to make only one phone call to the customer care. It was not a hassle at all. The customer care executives are also well mannered and very helpful. The phone banking services are good but you are charged 3 bucks for every SMS!
So, I would say that overall it is quite a convenient and easy-to-use services bank but the ATM thing is not very convenient.