Um, I'm by no means a big Sephiroth fan, but his trailer was possibly the most referential and reverential of the lot. Almost every scene was a callback to FF7 or Advent Children in some way, you can tell Sakurai really wanted to do him justice.
Joker and Banjo come close, but it's still Byleth for me. I was very pleased with the Three Houses rep, even if it wasn't the exact character I would have chosen.