if you don't know what AC is...it probably doesn't make sense to drop $200 router for it
when i was shopping for a new router few months ago..the guys at SNB forum all recommended buying what you need...AC1900 is basically beta testing while paying a huge premium...which looks even sillier now that draft AC has been finalized and 4X4 AC2300 has been announced
if you need USB 3.0 performance go for the AC56U..same internals as the 68U except its radio is 2X2 instead of 3X3...you can overclock them too
AC1900 First Look: NETGEAR R7000 & ASUS RT-AC68U - Storage Performance, Routing Performance - SmallNetBuilder
R7000 is a killer router...again I didnt wanna pay so much for a networking device and asus dev/custom firmware scene is unmatched...if you still with the AC68u go download merlin's build.