Just adding my 2 cents.
The best Ubuntu was 10.4, it had all the best things that worked great together. (compiz, nvidia drivers, gnome 1, firestarter)
But those days are over sadly.
Manjaro is great (have been my primary for a few years) but since I started using MX, I could not go back.
Yes sure you dont have access to AUR, but there are workarounds in MX.
The main issue with Manjaro is the package management. You will notice that it will break the system eventually, and its difficult to keep certain packages supported because they like to be bleeding edge, and not properly test everything.
MX has a few awesome features which I love.
- xfce with settings/tweaks app (manjaro also has this but not as nice)
- nvidia driver installer made easy (better than manjaro)
- boot loader fixer app (manjaro does not have this)
- grub-customizer installed by default and working as expected (manjaro had this few years ago but lost support)
- conky-manager installed by default and working as expected (manjaro also have this)
- easy way to install and switch window managers (manjaro can also do this but more fiddly and not as stable)