This is Pickles, my favorite duck. Roughly 13 weeks old in these pictures. I thought he was a drake for a while but have become less confident over time. I have two other muscovies who I'm pretty sure are drakes, but comparison hasn't been particularly useful since they are from a different clutch about a week younger. I have no confirmed female muscovies to compare to.
Pickles is the biggest of the three. However, 'he' also has a pointier tail than the others, has the smallest feet (barely, about a half centimeter difference), and has the thinnest neck (but not dramatically so). The main thing tripping me up is that Pickles had full flight feathers at 12 weeks, when the brothers still had pin feathers.
I tried posting in some Facebook groups and there wasn't really a consensus on drake or hen.