Naginata all the way, if the other choice is the chainsword as pictured.
Here's why: The edge of the chainblade does not align properly with the knuckles of the model (you did it with the naginata blade) and the hand guard of the blade kind of negates the benefit of the long pole. Someone using that kind of weapon would have difficulty sliding the hand up and down the pole.
If you fixed these issues, I would still vote for the naginata blade but it would be a lot closer. To me the sleek look of the rest of the model harmonizes better with the naginata blade than with the blocky, crude chainblade.