I've been viewing this thread since it began and only now felt the need to reply here.
I sincerely think that right now superiority is clear, and it is Wyverii's sprite that has the lead.
Now for defending my point, firstly assuring you all that I'm trying a completely constructive approach, please do not take my criticism as offensive.
I did not like KoA's first sprite at all, and the problem is that everything I didn't like about it is back in his second sprite, meaning:
The legs and feet are extra bulky, and the legs are bent strangely in this pose, the toes seem out of proportion, with different sizing for each, and the head positioning is a bit odd.
On the positive side, it has extremely well aplied shading and the arm canons are just perfect.
Now for the reasons why I think Wyverii's is the best:
The head is very good, the wooden fangs make a great detail, there is great coloring and the wood is perfectly detailed. But the one trait that caught most of my attention is one so subtle that I bet some people didn't even notice, and the level of detail it adds contributes to a great realistic look, I'm talking about the claws in it's toes, extremely well executed, giving it that "I need to carve them in the ground to shoot my canons without worrying about propeling me backwards" look.
On the negative side there is the strangely positioned tail.
If I can give advice for improving Wyverii's fine art, the only thing I have to say is, try changing the shiny version's leaf colors to a red or brownish dry leaf coloring, like they were in the fall or something.
Good Luck!