The R6300 doesn't offer quite as many features as Asus's 802.11ac router. It comes with a DLNA-certified media server, built-in Samba and ftp servers, and parental controls via OpenDNS (much like the D-Link DIR-865L); but it lacks an iTunes server or VPN pass-through. Like the RT-AC66U, the R6300 does provide guest networks on both bands (Buffalo's WZR-D1800H doesn't provide a guest network at all).
The RT-N66U is not a 802.11AC router I believe?