Here is how I see it:

Beginners:
Linux Mint
ZorinOS
SolydXK
Netrunner

Intermediate:
Ubuntu
openSUSE
Mageia
Manjaro (mainly due to its arch base and occasionally having to compile)
Sabayon
Debian
Fedora

Advanced:
Arch
Gentoo
Slackware

Holy crap this is hardcore advanced:
Linux from scratch