At this day and age there is no reason to continue using Ant. Ant was a great tool for its time but this time has passed.
There are basically three build tools that can replace Ant: Maven, gradle and Buildr.
It is important to be able to continue using existing Ant scripts and custom tasks alongside the new tool. There is a multitude of useful open-source custom Ant tasks and with Ant being a de-facto standard for years, many development shops built vast libraries of Ant scripts and custom tasks.
Out of all three, Gradle has the best integration with Ant. It allows for using existing custom Ant tasks pretty much without any changes. It also allows for importing Ant scripts into Gradle build script. Gradle tasks can even depend on Ant targets (and vice versa). There is also easy access to Ant properties.