Here is my experience

I am in Delhi and a broadband user for last 2 years. I have used Sify, Tata Indicom and now Airtel. Let me tell you all the three suck for different reasons. I am using Sify for all 2 years. Used Tata Indi for 3 months last year and now using Airtel BB for last 2 weeks. Here is my experience:
Sify:
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Plus - Speed has never been a problem. Almost always get near about the speed of 256 kbps and sometimes even more.
cable operator is on call 7 days a week.
Minus - Last mile is handled by cable operator and cost cutting is the name of the game for them. Untrained staff, bad cables and frequent downtime.
Tata Indicom:
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Plus - Excellent speed.
Minus - Bad customer care and support. I had to email the Country Head for VSNL broadband services to get things working. Infrastructure is not up to the mark.
Airtel BB:
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Plus - Excellent customer support. Get he cell number of the local engineer and you never have to call crappy customer care execs.
Minus - Pathetic speed. If you buy 256 kbps connection, they give 128-256 which mostly works around 128 kbps only.
In last 2 weeks I have never seen above 192 kbps try as hard as I might.