Personally, I always preferred Sean Kanan's AJ. He was more believable as a Q than Billy Warlock's AJ.
Don't get me wrong....I LOVE Billy W.!! I would have preferred him to be a new GH character altogether. In fact, it would be cool if they could bring Billy back as another character. He was just too different from Sean at the time to fit into the role of AJ. It might have been different if he had originated the role.
At any rate, I'm excited to see the havoc his return will bring, particularly with Carly and Michael (and Sonny, of course!).