I like Lumine better as Abyss Princess because her gown can pass for a Princess outfit. While Aether's crop top is pretty

I like Lumine better as Abyss Princess because her gown can pass for a Princess outfit. While Aether’s crop top is pretty common for JRPG protagonist or villain, the standard brown leather doesn’t look regal enough to be Abyss Prince.

Then there’s the voice acting. Both sounds determined but Lumine sounds cold while Aether still sounds innocent. Whether by righteous anger or Abyssal influence, I feel Lumine’s acting fits a villain better.

Although Aether’s innocence makes you question if he’s in the right, so it works as a mystery, a hint that he’s a hero in another story is the truth.

So it still depends on what you prefer.

I prefer the implication that Lumine’s coldness being that she’s influenced by Abyssal power, which fits that trailer where the Princess have been tricked, on top of the more regal appearance.