Airtel's USP has always been reliability, there should be no issues provided the wiring in your area is good, it is best to ask a neighbour who has been with airtel to get a fair idea. As far as response time, they are pretty quick there too.
The one area airtel has always sat on the fence with is their plans/pricing, though with stiff competition they have been forced to get off that fence and be competitive. One thing is certain, airtel always reacts to others, they have never taken the lead to shake things up.
As for the speeds, another thing airtel is great at, 40Mbps means you will get 40Mbps if not more than that at all times.
Don't be too worried about the wires, if the existing wires in your house cause issues, they will gladly replace them to get your issues sorted.