As someone who tried both, I think Endevour is better. 1.It's more bleeding edge. 2. It's as close to vanilla Arch as you can get with a gui installer. 3. The dev team seems to be more compitent then the Manjaro team (i.e: shit doesn't break because someone pushed a WIP package). 4. Better community support (I mean, it's literally just Arch with a fancy installer).
They're both fairly easy to install. And it's fairly easy to switch between the two.
You have to remember that most people aren't power users. A lot of people find if difficult to even install Windows. Vanilla Arch isn't for everybody.