the catch with fbx is that one company controls it and that it is no format with open specifications but just a closed software library you can use.

collada (www.collada.org) would be really free/open. i think they also have open source c++ code to read/write the format.

the catch with collada is that it is relatively new and not as widespread yet. the max and maya exporters are supposed to be very good already though. this looks more like it becomes the standard to me. it is much more tailored for realtime 3d than fbx.