appengine-maven-plugin is nice because it's the official Google version, but unfortunately it looks like support is not very good. They don't have contribution guidelines (see my issue here https://code.google.com/p/appengine-maven-plugin/issues/detail?id=44), they don't seem to fix reported issues. I've found a bug that keeps the devserver running even if you invoke the appengine:devserver_stop goal. I don't know if/when they're gonna fix it.

maven-gae-plugin, on the other hand, is unofficial. But it seems like we can have more control over it, am I right Brandon? Do you have the permissions accept patches and to release news versions of the maven-gae-plugin?