@Haiasi: Yeah, most of them are too clean. These are just roughs to try to find cool shapes.
I tried some more variations on the style of 8, but I don't think I like them as much as 15 and 16.
15 and 16 are in Darksiders Core style. The bottom is supposed to be a skull with spikes coming out of it. The handle will be a femur with leather lashed around it. I might make a skull between the axe blades.
Here they are with the character scale comparison:
Which looks better - 1 blade or 2? I'm going to start detailing the concepts.