Lyn - I think would be very fun to play with, she has her bow and her sword. Her battle animations were so cool in the game.
Marth - I mainly choose him since sm4sh. I like the tip of the edge and his fluid side attacks.
Corrin - Lances are fun and dragons are cool.
Lyon - I don't think they would include him if it's not for a remake promotion but I think being able to summon a phantom would be interesting in smash. Also dark magic is cool but admittedly they've nailed nosferatu with robin anyways still I think he's a cool guy.