We've got reports from Linux users using KDE that fonts are not anti-aliased and looks bad. To fix this add the following Java property in Tools->Tool Properties and the General category. In the Specify Overridden Java VM Properties here add the following on a new line, click OK and then restart DbVisualizer:
-Dawt.useSystemAAFontSettings=on
If you are launching DbVisualizer using the dbvisgui.sh script, you need to edit the script and modify this row:
VM_ARGS="-Dawt.useSystemAAFontSettings=on -Xmx2048M -XX:StringTableSize=1000003 -Dsun.locale.formatasdefault=true $VM_ARGS"