AppImage is great, definitely the best of the bunch.
AppImage solves the packaging problem in a bad way (ugh, loopback mounts), but does not solve the dependency problem, try run AppImages compiled for Ubuntu on Fedora..
[Retort insult.]
AppImage is just the least bad solution - if nothing else it doesn't need some weird infrastructure to run. As a developer you just upload the binary to your site and as a user you just download the binary and run it.