Now to put it simply, Debian/Ubuntu based distros are often seen as more user friendly, apt has more packages in it's repositories than pacman for instance. On the other hand, pacman is faster and simply a better package manager in my opinion, more clean, easier to use and faster.
Then there's the arch user repository which provides more packages (compiled from source) than apt is seems. That's an unbeatable feature, plus that Arch based distros comes with the most recent versions of every package while Debian/Ubuntu can have many years old packages that only receives security updates.