As a user I don't like neither Snaps (that for sure as this is Cannonical only) nor FlatPaks (as they seem conceptually a "80% solution" which combines the problems of package systems with the problems of self-contianed apps, but don't improve on anything).
For me the only acceptable solution besides proper .debs are AppImages. AppImage doesn't try to "replace" the package management for desktop apps like the former two candidates. It tries to complement package systems for some special cases (like for example commercial software, or for the cases where the user "just wants to try something out" without "polluting" the whole system with a lot of dependencies).
For my desktop needs AppImage is like "Docker, the good parts". A simple self contained format that runs everywhere without any further dependencies. Compared to that Snap and FlatPak are bloated annoyances.
For me the only acceptable solution besides proper .debs are AppImages. AppImage doesn't try to "replace" the package management for desktop apps like the former two candidates. It tries to complement package systems for some special cases (like for example commercial software, or for the cases where the user "just wants to try something out" without "polluting" the whole system with a lot of dependencies).
For my desktop needs AppImage is like "Docker, the good parts". A simple self contained format that runs everywhere without any further dependencies. Compared to that Snap and FlatPak are bloated annoyances.