Gradle covers the 80% use case really well. Everyone new to Android should use Studio + Gradle, no question. Dependencies are a breeze, the integration between Gradle & Studio is wonderful, the syntax is super simple, and the plugin handles most things by default pretty well. There are several things like build variants & package name interpolation that were impossible with Ant, difficult with Maven, and are trivial with Gradle.
The intermediate level stuff is more of a mixed bag. Some tests work well with Gradle, others (like Robolectric) are more of a pain. The NDK support isn't worked out yet. Some of the more fringe plugins like code coverage and formatting aren't plugged in yet. Here you will probably have to understand a bit about Gradle, but the tools team is making progress fixing the issues. What was a problem 2 months ago just works out of the box today with no Gradle specific knowledge.
For advanced things like writing your own plugins, then you have to know the respective build system. I don't know Maven well enough to write my own plugins. I have written a couple Gradle plugins. I have one that uploads APKs at the end of the build to various distribution APIs, one for secure signing, and one for bumping the versions whenever I want to. It was pretty straightforward to figure out.