The second language I'm considering is C++. This is the language that I use the most at my day job. It's also the language that's used to build the vast majority of computer games and one hell of a lot of commercial software. I'm not as familiar with it as I am with Java, but I know it well enough to be productive with it. I'm also familiar enough with it to know how horribly broken it is in many respects. One of the major design goals of Java (among other more modern programming languages) was to fix the problems with C++. It also has no dynamic capabilities what-so-ever, but it's possible to paper over this by using a minimal dynamic runtime such as Lua for scripting.
All things being equal, C++ is the fastest of the three languages. It is also the one you're most likely to write bad code in, though, so there's a bit of a trade off here.
As I mentioned, most games are programmed using C++. As a result, there is a veritable shit load of graphics engine options. I would probably tend towards using the open sourceOgre3D rendering engine (or something similar), but it's worth baring in mind that I could easily switch to using, say, the Quake 3 engine (open sourced by id) if I wanted to. I could also port the project to using a commercial graphics engine if I had the desire to do such a thing.
The measure of applicability to other parties is definitely a point in favour of C++. Code written in C++ would be the easiest of the three for deployment as part of a larger project, as that project is most likely to be written in C++. In terms of acting as a developer showcase C++ has the edge as well, as it's the language a lot of companies ask for code samples in.