Aria is a former evil-sea-serpent turned teen brat, although I see the appeal; Autumn Blaze is a cute, kind, funny and determined Kirin who protects her friends,
I'd go with Autumn Blaze, my second favorite character introduced in season 8(She's behind Smolder), and one of my all-time favorite characters. Although I feel Aria Blaze is a bit underrated as she gets overshadowed by the other two Sirens. But without her, Sonata wouldn't be as funny.