I have no spending limits. I would like an all-in-one device (router and wifi access point) for home use (120 m2). I would like a 100% supported device. Among those for which there is already a complete image to flash without modifications with 100% functional hardware. I'm now on Linksys 3200ACM and it's still great. I purchased an Omnia, but it was a total disappointment in many ways (I'm selling it). What do you suggest me?
Maybe elaborate, since on paper this seems like a dream device?
Several people here like the R7800.
I will elaborate:
I have a Linksys, it is practically perfect, if it were not for the well-known problem of Wi-Fi chips, which have a proprietary and no longer maintained firmware. I appreciate Linksys for the dual-boot and the fact that it is 100% supported by OpenWRT and have a very simple OpenWRT installation mode. On the project page there is a hardware table. I would like to know if a device similar to the Linksys is listed, but with an open and supported wifi compartment. The power of the Linksys is excellent in everything: CPU, amount of RAM and storage. I have no big claims, I have a 1Gb / 100 Mb FTTH and I use it to connect devices with active sqm and possibly VPN.
hard to find, i have the wrt 3200 acm, and sometime i forget that device is in my home, it just work, a better device will be a wrt 3200 acm with 2.4 ghz ath9k card, lol.
If you decide to stick with the ipq806x platform (the one R7800 uses), and you love the dual-boot feature, there are also Zyxel NBG6817 and Linksys EA8500.
Both Zyxel and Netgear are newer (I believe) and definitely more expensive, the EA8500 has been on the market longer, so can be had used for much less, however some newer ones (marked as the same revision as the original ones) come with encrypted firmware and without soldered headers, making it harder to flash OpenWrt on it.
The EA8500 may be an option if you find a cheap/ used one, but it uses the older ipq8064 chipset (instead of the faster ipq8065 found in the r7800 or nbg6817) and has a few hardware/ design quirks that make it less attractive. Contrary to basically all other ipq806x devices, the ea8500 only uses a single CPU port to the switch (which the data has to pass twice for routing), while the other use two (one dedicated to WAN, the other dedicated to LAN).
That doesn't mean I wouldn't buy one for the right price, but unless it's much cheaper than the r7800/ nbg6817 I'd prefer the later (disclaimer, I own a nbg6817).
 that theoretically halves your full-duplex throughput, as this single 1 GBit/s CPU port becomes a bottle-neck. All data needs to pass through it twice - internet <--> [WAN <--> CPU <--> LAN] <--> your clients.
In reality both the Linksys WRT3200ACM and the Turris Omnia, which I own, have mvebu platform (Marvell ARM 32-bit). But any processor of equal power is fine with me.
Which Netgear? Above you refer only to Zyxel and Linksys.
I saw on Amazon and that Zyxel comes only 180 euros, much less than the Linksys paid 280 euros and the Turris Omnia paid 320 euros. Up to 400 euros is not a problem for me.
I would exclude this device precisely for the reasons you said, I can't risk finding a card holder in my hands.
Ah, thank you for the explanation why it may be cheaper.
R7800 which @neheb suggested.
I think you have something against Turris Omnia router as this is another and another thread from you, where you are saying it is a disappointment. In other places, you are saying that it is a good device.
So, to be honest, I don't understand your opinions. Yes, they can be changed over time. But for me, it looks like you are saying in the morning: "Yes, it's a good device" in one place and in another place after 10 minutes "It's a disaster!". So you can say at least why the device is not suitable for you.
You could just say: "I tried Turris Omnia and it is not for me. That's why I want another router".
Actually, it seems to me the best.
ath9k through USB
It can be done?
hahaha sort of. There are USB WiFi adapters that use the ath9k_htc driver, which is probably not a good idea to use as it's draft n.
There are also mt7612u USB WiFi adapters but the one I have has poor range.
It's possible but not recommended. Unless you really like devices with less firmware...
ath9k_htc supports ar9271+ar9285 or ar7010+ar9280, both of which aren't draft-n but the final specification, it's still not a good idea to use ath10k_htc 24/7 or in AP mode (quite some issues).
carl9170 ('otus') is the draft-n chipset, using ar9170+ar9101 (AR9001U-NG) or ar9170+ar9102 (AR9001U-2NG) or ar9170+ar9104 (AR9001U-2NX) - which isn't any better, combined with the silicon issues of draft-n wireless.
usb device in my experiences are never an option, only for monitoring
To add some data to this claim, have a look at @jeff's excellent performance charts over at https://forum.openwrt.org/t/comparative-throughput-testing-including-nat-sqm-wireguard-and-openvpn/44724/1 the ipq40xx is a r7800 equivalent if I recall correctly (probably EA8500 or so), the chart also contains two mvebu routers now.
Another vote the R7800... it just works/rock solid stability.
But compared to Linksys, it seems to me not very powerful and with little NAND memory. The flash procedure does not seem very simple to me.