IMO, it comes down to the rest of your system and some of your requirements. Specifically...
- If you are running multiple Unifi APs, a Unifi Gateway device, or Unifi switches, you may be best keeping everything in the Unifi ecosystem.
- If you need certain types of detailed statistics, Unifi may be desirable (collectd can do a lot, but I think their stats are a bit easier to work with).
- If manufacturer support is important to you, stick with Unifi firmware.*
*Regarding manfuacturer support, UI actually doesn't do much support on their end... they have forum where community members support each other. This helps them reduce costs, but can be problematic, too. They do offer hardware warranty support through UI proper, of course, but I have no idea what happens if they see OpenWrt installed when you do an RMA).
OTOH: - If your setup will have just one (or a small number) of APs, the Unifi Network Application is a bit of a PITA to run, and doesn't really offer much of an advantage. OpenWrt will be easier in terms of configuration and support.
- If you want the device to be more flexible in terms of running additional packages/services, OpenWrt is by far more capable.
- This forum is here to support OpenWrt... you're in the right place now!
Full disclosure:
- I used to be very active on UI's forums. I left when the UI staff undermined my advice (which was accurate and effiicent, but not what they wanted from a messaging perspective). I then devoted all of that volunteer time/energy to OpenWrt where I can help a true FOSS project that is not corporate/profit based).
- I still really like UI products. I run a full UI stack (router + switches + APs) on the vendor firmware.
- I love OpenWrt and use it for selected purposes, and of course I'm here a lot
