EPS is
a graphical format which is scalable. It means that when you zoom an
image, you don't loose quality. So this format gives good printing
result.
You can enable it by using
-teps
flag with the
command line.
You can also use
format="eps"
in the
ant task definition.
<target name="main">
<plantuml dir="./src" format="eps" />
</target>