Stella Vs Luna: which character seems more interesting to you?

[Nuvendil]

Neither is that overly interesting at this point frankly. The broad strokes are rather token to be honest; it's the nuance that makes the characters and there's not much there at the surface. I would go with Stella if only because there's some minor complications apparent at the onset as she is shown to be at times on Noctis's side and at others his enemy. But yeah, a bit early to start this debate.