RT-N18U is the best among all the N-series Asus routers but it doesn't has 5GHz 802.11ac.

Wireless AC is not common use even for me, I'm using RT-AC55UHP but the AC signal range is narrow compare to N signal.

Wireless AC has faster speed but narrow range, wireless N has slower speed but wider range.

RT-N18U should performs better and more stable than my RT-AC55UHP because this router has 256MB RAM. It has faster 2.4GHz wifi speed up to 600mbps.