I have old Debian 9 (stretch) installed long time ago. After installation the default fonts didn't look very good on display of the box.
I tried some fixes, for example put custom fonts.conf file in /home/username/.config/fontconfig. Also I'e installed a few new fonts, include Ubuntu. Now it looks better. I don't remember what fonts was in default installation. Which fonts looks better on Debian 9 with Xfce DE? Maybe there are some fonts, that looks better than Ubuntu, Noto Sans or Droid Sans?