On some systems LCD hinting gives better fonts, because this is not working on all system, this setting is not configurable through the interface. You can set it with a simple query.

xfconf-query -c xsettings -p /Xft/Lcdfilter -n -t string -s lcddefault

Other possible values are lcdnone, lcddefault, lcdlight and lcdlegacy. You can check if the property is set property, run xrdb -query in a terminal.