<p>From my small amount of experience, I've only used Ant as a build tool. Are there any other projects which are better, and why?</p>

Maven
It is much better than ant because for most common tasks you don't have to write a complicated build.xml, maven has very good defaults and it's all convention over configuration.
It has also a big central repository of libraries and it's very easy to configure it to, like, "use latest stable commons-whatever". Maven will then download the latest stable version for you (no more checking in jars into VCS) and if a new upstream stable version is released, it will download it as well. Of course, it's just as easy to lock it to some specific version should you need that.
It is also well integrated both with Netbeans and Eclipse (m2eclipse plugin) so the IDE honors whatever settings (including dependencies) you declare in the pom.xml file.
There are also some downsides to maven: some plugins are rather poorly documented, integration with both IDEs is not really perfect, and that in different ways, some error messages may be hard to understand.