Hello,
I've been using Maven for several years in different enterprise projects and could recommend it to you. I do not have any experiences with Gradle, so could not tell you which one is better.
However I can assure you that if you choose Maven, you will not be disappointed. You can quickly configure your continuous build environment using Maven together with Nexus and Hudson.
All of them are great products easily installed and maintained.
There is also another nice feature of Maven: plugins written in
Java. There are lot of thems: for example for managing dependencies, starting application server, sql operations.
If is not enough, you can always write your own plugin, which is easy and well documented.
And one more thing, as I can see on Gradle site, the last version is 1.0-milestone-3.
In case of Maven the last version is 3.03, You can also choose version 2.2.1 (I'm currently using it).
If you start a commercial project using stable version is a must IMO.
I hope this will help you making your decision