Thank you for your two cents
The second idea (the Empire of Evil) is in short but interconnected stories. I think I should try something like that for the first one too, because it seems to work better.
I did not realize that people cared about Marine and it's yet another reason that I do not drop this project for the other. I know there is something worth telling in there, but I don't know how to tell it yet.
On the other hand, if I choose the Empire of Evil, it only means that I will probably do the other one after it and it will surely be better by then