Jmonkey or Gameplay
Gameplay: Documented C++ API, Undocumented Lua bindings for scripting, minimal examples, no editor
JMonkey: Better documented Java API & internals, No scripting langage, great examples, has an editor
What's most important to you?
Gameplay is the smaller engine, so it's easier to understand the internals. It should also offer good performance for simple scenes.
JMonkey has a lot more features, and has a more sophisticated scene manager (scenegraph) so it should perform better in complex scenes.
What type of games are you looking to develop, and what is the scope? I guess my feeling is that JMonkey is going to be able to better cope with a large project, but Gameplay may be easier for a small project.
Have in mind that Java has a generally good standard support for scripting languages. So you get third party libraries like JRuby, Jython or LuaJ using standard APIs for scripting in their respective languages (Ruby, Python and Lua if it wasn't clear :P ).
Also if you have Java 7+, you get Javascript out of the box with the embedded Nashorn engine.
So you have various options to implement scripting in your game if you need to.
Hummm has someone take a deep look in GamePlay? ( I assume we are talking about http://gameplay3d.org )
I am studying OpenGL and some 3d engine/applications concepts... Someone know about gameplay internals?
Has it some good design concepts? May it be used as a good example of 3d framework ? I mean.. the design of internals, etc?