These are the original operating system files released by ZTE. They are the safest and most stable, but they are outdated (most run Android 7.1.2 Nougat or early Android 8.0 Oreo). The for users who prioritize call quality and camera stability will always be the final official build.

The official stock firmware is recommended if you want the dual-screen features to work perfectly without bugs.

If you are looking for "best" in terms of performance or newer Android versions, the community often turns to custom ROMs, though support for the unique dual-screen is specialized.