Personally, I admired work of WETA for LOTR, but I think, they have gone way to far in some things concerning the Hobbit. If you watch the videos showing WETAs work and ideas concerning LOTR, the main message is, that everything should still be beleavable and "realistic". For the Hobbit, in my opinion, they have forgotten a little bit this aim. For example I am pretty sure, that those crossbows would have not shot one arrow, if they were really built. And I am not even speaking of the extra weight all those boar stil elements represent.
So, I defenetly prefer Edain's intetpretation of the crossbows and also of the arrows.