Dark Knight.

Get two Iron Duke accessories from Trema, equip them both to whoever (...make sure your characters are all level 99), and with that, use the Dark Knight Dress Sphere with her, and you'll find that you can take on the Paragon almost single handed (...it's still close to impossible to defeat the Paragon with one character, even with that setup).

Though, I believe the Dark Knight gives you the best results. I've not obtained the Mascot Dress Sphere yet, I have all others except Mascot. So from that, Dark Knight (...it's easier to locate too if you're new to the game, compared to the Mascot Dress Sphere).