Ant and Maven are both great tools and have many similar traits and features. Ant is popular for its flexibility while Maven is popular for its management of dependency efficiency.
But the reason why Gradle is the first choice of many people is its unique traits. One of its best features is that it works commendably well on numerous multi-projects with easy to use functions. It possesses the key features of both Maven and Ant i.e. convention building and flexibility.
The other two have no support for multi-projects and you have to do a lot of coding.