Ubuntu 17.10, open last used window from group, when clicked in Dock
It seems that the behavior of the click action can be changed with:
gsettings set org.gnome.shell.extensions.dash-to-dock click-action 'cycle-windows'
cycle-windows is the closest behavior to unity.
You can list other values with:
gsettings range org.gnome.shell.extensions.dash-to-dock click-action