Send me a symbol and I’ll tell you the difference between AU and Canon. Then I’ll tell you which one is better.
Well, in canon, Aqua’s two best friends are Terra and Ven and that’s... That’s really about it! She makes a lot of friends along the way during Birth by Sleep but it’s questionable how remembered she even is at the given canon point in KH considering twelve years have passed.
In AU though, Aqua has a lot more friends-- although she’s not best friends with poor little Ventus (yet.) I’d say this is actually better as she is closer to more people and also has significant friendships with the other KH ladies, which don’t exist at all in KH and is one of my major gripes about the series. So yes. AU = much better.
In canon, Aqua is a keybearer under the tutelage of Master Eraqus and it’s implied she’s been there for a while along with Terra, and that’s really her, Terra and Ven have ever known. Which in theory is a pretty awesome lifestyle-- especially the kind the three of them dreamed about, with all of them being Masters some day-- but given the events of Birth by Sleep and the rest of the series it’s... It’s not all sunshine and rainbows. Still cool as hell, though.
In AU, Aqua’s life is fairly simple if sad during her childhood given that her parents died and she and Kairi were taken in by their grandparents. (However, I don’t think it’s a far stretch to say Eraqus took her in as an orphan or as a girl with neglectful parents in canon, so both could be sad, who knows.) She’s an overachieving college student, an athlete, a dutiful lifeguard, and over protective older sister. Given her canon background I’m sure she itches for adventure a little.
In terms of peace, AU’s better, in terms of awesome, canon definitely wins.