I thnk his '13 style is closest to what is considered his modern appearance, and I could totally see him entering Smash with it. His Garou: MotW look is quite unique for him though, and I think it would make for an awesome alternate costume for him.
Though Fatal Fury is where he originates from, he's one of the primary faces of the King of Fighters franchise now, so I could see him having the gameplay from that series more than any other. He would make for a great counterpart to Ken as well, considering they've been friendly rivals in the Capcom vs. SNK games, where they even share a special intro before they fight:
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On this thought, I'd really love if other fighters in Ultimate shared special openings with each other, as unlikely as that is to happen. That would be really awesome if it could be done though, and would help bring out each character's personality more outside of a potential story mode.