Though I prefer having Jenna, Alex would be pretty good. He being a villain and all that stuff increases his chances indeed. And remember, he's the only one in the whole series who can modify his own thoughts when you read his mind xDDD
My only problem, would be with his move set. Since we haven't actually seen the extent of his power, and so, only standard mercury psynergy could be implemented for him.
His Final Smash would most likely be him using his part of the Golden Sun to go super powered for a short while. Although I don't know, if he can use it, while Isaac has part of it.
Golden Sun 3 please Camelot!