I've been running a RT-AC68U for a while. Rock solid stable on Asuswrt-Merlin[1] (204 days uptime last I checked, and the last reboot was due to a power cut, and easily get 50MB/s to my file server over wireless). The Asuswrt interface is a little clunky, but once it's set up it works fine. I've recently changed to Tomato (needed VLAN tagging for wireless), which seems just as solid (55-60MB/s to file server), but I haven't tested WAN/NAT performance (moved to a pfSense box).

[1] DD-WRT struggled with 100Mbps to WAN - hardware NAT