which one will win in the long term: snap or flatpak?

snaps are focused only on ubuntu and official ubuntu flavours (mainly due to the fact that it requires a specific apparmor, or it will run in classic mode, without sandbox). they are way better for people using it in enterprise compared to flatpaks, and support CLI. ubuntu core (the immutable version), also uses snap kernel and snap gnome.

flatpaks works on any major distro, but they only support GUI software, and there is no paid support for them in enterprise world (if you pay for ubuntu pro and have a problem with snap packages, a canonical employee will help you fix it.)

which one you think will still exist in the next years? imo: snaps, they are worse, but have more use-cases.