I like UIs that feel premium. Needless to say, Xubuntu and i3 do not make the cut. Left with Gnome 3 (ugh) or KDE (options galore). All other DEs feel clunky (graphical glitches, sub-par design) and are also usually buggy (which is normal for an open source project with such a big scope).
XFCE looks a lot better with a different window theme installed, the defaults are absolutely terrible. There's as many options for XFCE as KDE, but it definitely takes tweaking before it looks good.
i3 is generally used for its productivity benefits, not for appearance. You can still spruce it up with a new bar (see Lemonbar or Polybar), but overall people choose it because it feels nice to use. The people on /r/unixporn have done a pretty good job of making it look good though.
