The last year I have gone through three routers:
* Asus RT-N66U ("the Dark Knight"), worked fine on 2.5GHz, but the 5GHz signal gradually became worse until one day it just disppeared. Apparently a lot of users have had this issue.
* Asus RT-AC66U, the smaller version of the same router. Just stopped working occasionally, requiring a reboot.
* Netgear AC1750 R6400-100NAS (little brother to the "Nighthawk"). Current router, was stable enough for a while, but now needs rebooting a couple of times every week. SSL/TLS connections stop working randomly. Devices such as iPhone and AppleTV fail to get packets through on the first try after being dormant for a while.
At work we have the Netgear AC1900/R7000 "Nighthawk", which has been extremely stable. But it's also quite expensive, and large (as is the AC1750).
I've lost all faith in Asus, and the only other brand I can see that has a good reputation is Ubiquity. They make "pro" access points for hotels and such. Then again, hotel wifi is the worst.