My vote would've gone to Dawn, actually (but the voting is closed now). I don't remember much of the story and I agree that Aria was more memorable in that regard. However, I disagree a little on the level design aspect... Parts of Aria was really lazy. The floating garden, for example, was pretty terrible.
Dawn had some really great boss battles, better than those found in Aria (IMO).
All in all, Dawn took a great game and made it even better. It wins no points for originality though, and storywise it did nothing interesting. They should've made it a separate game instead of a sequel. It could've had someone else as the main character, taking place in some other time. Dunno... Maybe it could've been Soleiyu's game? Remove the modern elements, such as the cars, get rid of the soul system in favour of something else, and change some of the cast + the storyline. Done!