When you are using modems you have to check your ISP to see which they support, ADSL is not so much a issue but VDSL can be done in a couple of ways and some routers do not support the method used by the ISP.
In any case buy a modem/router that matches the service the ISP is offering. Does you little good to buy a router that supports vdsl or adsl2+ if your ISP does not offer the service.
There is little difference in the price of the radio chips for 802.11n and 802.11ac now days. You likely can get a basic 802.11ac for about the same price.