Wireless AC is the latest wireless standard and provides the fastest speeds. Your wireless devices need to be 802.11ac compatible, otherwise you will be using the slower Wireless N technology.
As mentioned, Asus have some well reviewed routers (I have an RT-AC68U and can vouch for that), but there are some other gems as well, notably from Netgear:
Asus RT-AC68U - http://bestwirelessroutersnow.com/asus-rt-ac68u-ac1900-review/
Netgear Nighthawk - http://www.netgear.com/home/products/wirelessrouters/ultimate-performance/R7000.aspx#