Debian fonts are just plain ugly. In fact, Linux fonts in general are pretty ugly. Ubuntu has done a nice job making its fonts look nice, but unfortunately those changes don't always get passed on to other distributions. To make the fonts in Debian look nicer, create a file named .fonts.conf in your home directory with the following contents:
<?xml version='1.0'?><!DOCTYPE fontconfig SYSTEM 'fonts.dtd'><fontconfig> <match target="font"> <edit mode="assign" name="rgba"> <const>rgb</const> </edit> </match> <match target="font"> <edit mode="assign" name="hinting"> <bool>true</bool> </edit> </match> <match target="font"> <edit mode="assign" name="hintstyle"> <const>hintslight</const> </edit> </match> <match target="font"> <edit mode="assign" name="antialias"> <bool>true</bool> </edit> </match> <match target="font"> <edit mode="assign" name="lcdfilter"> <const>lcddefault</const> </edit> </match></fontconfig>Log out then log back in to apply the changes. The fonts will then look so much nicer.