Wu v2 is probably the best hands-off quantizer that I have seen. It's not the fastest and probably too resource intensive for embedded apps, but it is remarkably good. I would recommend it (or anything based on it) without hesitation.

I'm actually in the process of porting it to js using typed arrays and possibly WebGL/GLSL. You can compile it pretty easily to asm.js for max pure-js perf via Emscripten, but I don't know how clean its API/interface will be and if it will leak globals based on how the code is structured [1]

[1] http://www.ece.mcmaster.ca/~xwu/cq.c