User blog comment:PacmanIsGr8DontH8M8/Season 6 Finale - Enter Your Combatants/@comment-27914891-20160228172843

Either Flandre Scarlet or Megumin.

Flan-Flan would probably last the longest.

Megumin could entirely blow everyone up if their close enough. She can take a large chunk of the competition away but then she's completely helpless.