The following is my personal recommendation.
If I were to buy a router today, it’d be AC86U, not AC88U because the former uses newer hardware, the prevalent positive reports in my local computer forum, and the possibility to run Merlin firmware.
I believe buying a WiFi router is like buying a computer - look at the CPU, and more importantly the WiFi chips, known defects, and firmware. Generally Broadcom is safer, but there are exceptions. The best example is Quantenna. This is the greatest source of the problem with AC87U. I can understand @Mike_O_Neill frustration with it but there is a valid reason for it, and not necessarily representative of Asus Broadcom routers. Netgear R7500 used Quantenna as well. Guess what - they could not fix the problems with the original hardware, so they came out with R7500V2 using a totally different hardware design, dropped Quantenna and replaced it with Qualcomm.
Even if I like the Asus GUI, of the dozen or more Asus routers, I’ll only recommend particular models.
The AC66R mentioned above is a Best Buy version of AC66U. This is replaced by the AC66U B1, which upgraded the original old MIPS CPU to a newer ARM CPU. This new version has much of the functionality of AC68U, so I consider it to be a budget choice.
Currently I use a Netgear R7000 but its firmware failed to do something I need stably, so I run a hacked Merlin firmware on it, which in turn is based on Asus firmware.
The AC68U was good, but the original incarnation had a hardware flaw with the USB 3.0 interfering the WiFi. So the firmware fix is to slow down the USB 3.0 significantly. The latest AC68U C1 uses a faster CPU and fixed the USB 3.0 problem, and thus have hardware equivalent to the R7000 I’m using.