Use the right tool for the right purpose. Maven is a black box that does many things extremely well, provided you can find a plugin that does what you want. For anything else I use Ant because I can get Ant to do just about anything without having to resort to writing a plugin, and I have used Ant for some fairly strange things (e.g. scheduled backups, building release images of a fairly large software stack).
However, now that I have used Maven, even the
Java projects for which I use Ant have the Maven directory structure. Or a slightly modified form thereof. Check out the build scripts for
JBoss in Action.