AppImage is my first choice because each image includes absolutely everything you need to run a program with no pre-installed infrastructure.
Snap is my second choice. With Canonical behind it, it has a lot of really sophisticated functionality. Ubuntu Core can only run snaps, and snaps maintained by Canonical get a green check mark.
Many Gnome apps are available as Flatpaks.
That said, I don't like using any of these when packaged by an unknown party 🙃