I voted for Arcanes: The Seer. Both sound really interesting, but you're far enough along with Arcanes that you can begin to write that while being able to switch to Heart of the Gods and work on developing it further if/when you run into a snag.
I'd say, do both! Just not at the same time. Do Arcanes: The Seer because your further along with that one and submit that one to the writing compensation. Do Hearts of the Gods another time. Both are really good ideas and you should do both of them.
Fair enough. One of the pros of working on Arcanes is that I have a proper beginning and end mapped out, and I'm organising everything in the middle. Though I tend to find the middle can be some of the hardest parts of the writing process. And you're right about how I can go back to develop the less defined story if I get stuck on Arcanes. ^-^ Thanks! That appears to be common reasoning from most of the people I've asked and it does seem to be the most logical route to take. As you said, I've gotten further with Arcanes, so I'll probably have an easier time actually writing that story than with Heart.