Based on this poll, I think my number one pick would be Nightmare. He would be a superheavy swordsman with great frame data, power, speed, and overall would make the likes of Cloud, Ike, and Shulk eat their hearts out with his Soul Edge. Nightmare is a humorous case of being both a pub stomper and a competitively viable character in most Soul Calibur games, which I'm sure would make him highly played. Of course with this in mind, there is a good chance of a character like Nightmare being considered overpowered if kept faithful to how he plays in the games, so there could be some balancing issues. I just find him to be a fun character in his own series, and hopefully it could translate well to Super Smash Bros.
Other than that, Heihachi is a very clear pick. He almost made it into Smash 4, but Sakurai had issues translating his fighting style from Tekken to Smash Bros. I've always been a fan of Heihachi, and like Nightmare I think we could also benefit from more villainous characters in the game. Heihachi seems like one of the more realistic choices for DLC as well, and man would I love a Tekken stage and music in Smash Bros. But like with Nightmare, Heihachi's game series does use a lot of combo inputs to achieve maximum effectiveness, and if done faithfully could be either too difficult for most players to use, or overpowered. Still, Heihachi's always been a favorite of mine, and I would be ecstatic to see him in the game.
Besides that, Lloyd Irving from the Tales games would be cool so we finally get a dual-wielding swordsman, which I think would be unique to a fighter's style in Smash Bros. Agumon isn't a bad pick either, although to make him faithful, digivolution would be a must. It would have to charge up like Cloud's Limit I'd imagine, although there's also taking into consideration adding Greymon, MetalGreymon, and WarGreymon as upgradable forms to achieve. If the digivolution mechanic is too complex and impractical to implement, then I'd just go with Omnimon, who would have a good mixture of a sword and projectile style of play. Digimon is a tricky case for me since I am a fan of the series, but making it faithful in Super Smash Bros would take a lot of work to pull off right. Also if Agumon ends up seeming too similar to Charizard, then a different Digimon could be chosen to represent the series, which I wouldn't mind either.
