Oooo, you're right, so many good options. Boba Fett instantly comes to mind for me too, specifically this version from war of the bounty hunters:
I mean the vibes are outstanding. Vader is iconic but I'm not sure the word 'aesthetic' really works for him. Really subjective I guess. Padme, Lando and Maul also come to mind all for completely different reasons. Din Djarin does have a strong aesthetic, if a bit of a boring one. Maybe I'm a bit biased after just finishing Andor, but Mon Mothma looked fantastic in every scene she was in, and she definitely wore very similar dresses that gave her a very particular aesthetic.
...or maybe Genevieve O'Reilly is just gorgeous.
When it comes to an aesthetic that really feels like Star Wars, though I think Boba is my pick.
Vader is definitely iconic and his look is such a staple in the Star Wars franchise. It's just that to me the word aesthetic implies a sense of style or at least intention. While Vader's look is a very strong aesthetic, I think that Vader as a character isn't very aesthetic because he's sort of just wearing what Palps put him in and he has no real intention to the way he presents himself. On looks alone, I think Vader is the obvious choice... I think I've just overcomplicated it for myself lol