Even we have experienced the same with Dlink router. It also used to drop the signals repeatedly. That was really disgusting. Things got better with Airtel and the speed also increased a lot. Now it has been almost four years, and we have not yet experienced any signal dropping.
I would suggest to go for Airtel, but they need to have a tower in the place where you stay in. For our relatives they denied to come.
That is a real headache, if they do so.