why are you installing a desktop environment
probably because he wants to
no arch is barebones
what desktop enviro do I install?
gnome? unity? ?-?
unity is a pain in the ass to maintain on arch is it depends on a whole bunch of ubuntu-related packages, you can pretty much always expect it to break after a new version releases. unity's great but it is
very distro-dependent.
gnome is alright, it's very heavy on resources and not very customizable (think of it like the OS X of linux desktops), but it's easy for beginners.
LXDE is super lightweight and basic, openbox even more so
MATE is essentially what GNOME use to be, it's rather nice. XFCE's similar, but a little more lightweight.
https://www.reddit.com/r/unixresearch might help you decide
