Tata sucks! I had it for about 4 months a year ago, and a friend of mine had it for 3. My friends connection was down for weeks at a time. I wasn't that unlucky, my connection went off for about 12 hours every 4-5 days after the first month. For the first month, the connection was like a dream come true.
But, calling their help desk was a nightmare. Dialing the number some 20 times before getting through, then having to wait for literally 20 minutes before you had your complaint attended to. And another day before someone fixed the line.
I have an airtel unlimited 256k connection now, and I love it. Have had it for a year, and it's rarely given me any problems. And though their help desk isn't manned by geniuses, it managed to solve all my problems, without getting me aggravated.