I am using airtel from 1 month and I am impressed with the network coverage it gives to their customers. Its network comes under metro also and never fluctuates during traveling. But as I mentioned nothing is perfect after 100mbs left the network automatically drops down from 3G to 2G. I think this is a drawback of airtel else network coverage is excellent.
Conclusion : network coverage is excellent, internet speed is good ( after 100 mbs left the network auto switch to 2G) else speed is good.