I’ve been using arch for a while now and I always used Flatpaks for proprietary software that might do some creepy removed because Flatpaks are supposed to be sandboxed (e.g. Steam). And Flatpaks always worked flawlessly OOTB for me. AUR for things I trust. I’ve read on the internet how people prefer AUR over Flatpaks. Why? And how do y’all cope with waiting for all the AUR installed packages to rebuild after every update? Alacritty takes ages to build for me. Which is why I only update the AUR installed and built applications every 2 weeks.
I am using both of them without any problem.
The main advantage of Flatpaks (and things like AppImage) is that you have a single “executable” with everything you need and sometime that is useful even if the software is Opensource but the building dependencies are a nightmare. Subsurface (a dive log software) is an example.
If the AUR package is a simple build (or a binary which is a converted package) then go for it. If you need to start building a lot of additional package from AUR to meet the dependencie then I would suggest, in order, to look for the Flatpak (or AppImage) package or to install an helper to build the packages