Hey Dlean,
If you want a library with good docs the Away3D's AS3 docs are good and should translate to haxe well, I've used this in the past for simple projects without much friction (although I did have the occasional bug).
I think heaps has a lot of promise, I've had a play around with it before and it looks great but of course it's still a wip the docs are in early stages so it'll be a lot of figuring it out on your own.
I've not yet tried babylon
What platforms are you targeting? If you're targeting the web primarily then three.js is worth a look into - I'm currently using it with externs and finding very nice to work with. Three.js has a relatively large community, which helps a lot when it comes to solving library-related problems. It's also very feature rich.
If you want to try three.js I can mail you some recent externs (built some for r71, not yet released)