I am looking for a somewhat detailed explanation of which 3D Engine for Actionscript3 is the most efficient, practical, scalable, documented, community supported, etc. When
The thing is, that papervision has a good community. In long term usage, you should take that into account.
I was the same in the beginning. It was not obvious where to find what. But you should stick with it. I just worked on a prototype: Papervision3d + Jiglib (3d physics for flash, ported from c++) and SmartFox Server = fun mulitplayer game :D
Anyway: this might help: http://papervision2.com/tutorial-list/