Since I've already spent more than 1 year and a half in Mumbai (Bombay), I know quite a lot about broadband market here, so I will try to make a kind of short review of local providers, from a point of view of a foreigner (who is used to a high standard of similar services in Europe).
For every provider I will specify 3 main ratings - quality of connection including stability and speed, price, customer support including how easy it is to connect to the provider. Rankings are given on a scale from 0 (worst) to 10 (best).
Tata Indicom - Quality 9/10 Price 5/10 Support 5/10
Details: Tata offers the most stable broadband in Mumbai. You always get 100% of the speed mentioned, at any moment. Cons: Tata is costly, perhaps the most expensive broadband. Support is quite slow - by the time they react (1-3 days) the problem is already solved usually. More cons: Tata is switching many clients to Wimax (wireless) technology so upload speed is always low - around 256 Kbps, even if in the planet it's specified higher. Installation time - sometimes as short as 1 day.
Tata owns inter-continental cable network through acquisition of Canadian TeleGlobe, so there is nice speed with South East Asia and Europe. Not so good with the US.
Reliance - Quality 7/10 Price 8/10 Support 5/10
Details: Reliance is the only provider that provides true symmetrical connection - download and upload speeds are equal. Big cons is that at least every week the connection is going down for a couple of hours or more, and customer support doesn't give any comments on that. So you cannot rely on Reliance, despite the brand name ;-) Reliance is almost twice cheaper than Tata - which is a very big plus. Support is slow and stupid - they only give you generic, "template" answers - no matter what you're asking. You say my connection is down - they will recommend you to reboot your PC, and so on.
Reliance owns an inter-continental cable network through acquisition of Flag Telecom so it's a 1) giant provider 2) doesn't depend on any other providers. Connectivity to South East Asia is especially good.
YouTelecom - Quality 3/10 Price 8/10 Support 3/10
Details: This is, perhaps, the worst provider I experienced. Speed is unstable - going up and down every minute, you don't know whether it's 1 Mbps or 128 Kbps. Also, broadband goes down quite often and no comments or notifications are given. Price is good - YouTele is cheap. Support is SUPER terrible, I literally waited 1 month and a half for my problem to be solved, even though it could be fixed in 2-3 minutes.
Tikona - Quality 8/10 Price 8/10 Support 5/10
Details: Tikona network is based totally on wireless technologies, so coverage is quite good. Speed is good and stable, but connection goes down almost every night, for some time, no explanation is given by the company. Price is good - rather cheap. Support is not 24 hour per day as Tata or Reliance - which is a disadvantage.
MTNL - Quality 8/10 Price 9/10 Support 3/10
Details: MTNL is a governmental, old fashion company but they offer cheap DSL services with some great plans - up to 4 Mbps unlimited. Nobody at the company speaks English so ask your Indian friends to help you :) You will need to bribe some technicians to get your connection faster, otherwise it may take up to 2-3 weeks. Another disadvantage - you must have an MTNL landline, since it's DSL. Connection is quite stable - up most of the time. Speed is exactly what you're promised. MTNL gets IP connectivity from Tata. Another disadvantage: upload speed is shockingly low on all plans - 256 Kbps. I tried increasing for an extra fee but MTNL ignored my request.
Hathway - Quality 9/10 Price 7/10 Support 5/10
Hathway is a rather small companies, comparing to others mentioned above. Connection is very stable (actually never went down) and speed is always 100% of the promised value. Price is good - it's one of the cheapest broadband. Support is weak - it seems like there are 2-3 persons in whole Mumbai taking care of clients. Installation time is quite fast - 2-3 days. Upload speed is terrible - not more than 256 Kbps, no matter what is your download speed. Hathway gets IP carrier from Tata, as far as I remember.
In sum, I would say that Tata Indicom is the best provider, if you can afford it. Another great thing about Tata, is once you become a client - you can use Tata Wi-Fi at caffee shops allover Mumbai, using the same login/password as for broadband.
If you are a developer or just need good upload speed - you have no choice but to go for Reliance - other providers suck at that.
A sad fact, but we have to face the reality, is that customer support SUCKS everywhere - at all of the mentioned providers. Customer support is absolutely unhelpful, silly and slow. In my experience, they NEVER helped me with anything. They just kept giving some standard answers, perhaps written above their monitors.
And never, never contact YouTelecom!!