16.0.5.3 of course. Why build 16.0.5.1, a later version if there is a newer version 16.0.5.3 with a corresponding stable release from yesterday? Did I somehow create confusion to imply that?
I don’t know if the tb-updater would still fail during the Qubes build process. For test builds could use --tb open to avoid a failing Tor Browser downloading breaking the build process but then Tor Browser might not be including Tor Browser. tb-updater however should work in the resulting image.
There are many improvements in the developers repository but also a very few remaining unstable things. So not yet in testers.
Building Qubes-Whonix from the testers repository would result in upgraded Debian and Qubes packages. None of the developers repository package upgrades are security critical. Only enhancements.
I planned to attempt a new Qubes-Whonix build once everything is stablized.