I'm not being sarcastic but I'd say openwrt 18.06.01 is the best firmware for this router. I got one of these a couple of months ago and couldn't get the 5ghz radio to work at all in dd-wrt. Others have but it's a pain. I'm not crazy about the Openwrt GUI and would prefer to use dd-wrt but it just didn't work well for me.
Newer firmware are also apparently too big so you need to flash to an older version first (something like March 2017) then upgrade to the newest one.
I've owned a 1900ACS v1 for a few years now. 6-12 months ago, I would have agreed with ellick. But these more recent builds of dd-wrt have been very reliable and I've had no problems with the default settings on the 5GHz radio.
Were you able to install that to the router or do you still have to install an old build first? I think I last tried installing the newest build back in September or early October and it would appear to install but actually wouldn't. I had to first install a built from March then upgrade.
The stock firmware still has a limitation (bug?) that prevents installation of firmware files larger than 32MB. So yeah, if you're installing from stock, you need to install an old version first, then upgrade.
