First you need to find from Airtel if they have any plan of upgrading to VDSL in your area in next 1-2 years.
@billubakra purchased TPLink ADSL modem which is not compatible with VDSL & Airtel has upgraded all connections in his area to VDSL.VDSL modems are costlier & lesser in number of models available so if ISP is providing one at cheap rates then it is better to get it from them.
A router is used to distribute connection,it is just that in case of ADSL/VDSL connection you will have to setup the modem in bridge mode & then connect the lan wire from modem lan port to router wan port where you will enter your airtel connection username/password using which router will make the net connection.You can use a modem+router combo device but combo devices are usually costlier(& dual band are very much so).
I am using Archer C20 & its range & performance(talking about N band performance) is a bit better than 841N I was earlier using.It was available for as low as 1100 during recent sales.Its 5GHz band performance is also fine for its price.Remember 5GHz is meant not for range but for bandwidth so you put your heavy bandwidth consuming devices like PC on 5GHz band while keep using mobiles/tablets etc on 2.4GHz band to avoid network congestion.