DIFFICULTY
Okay, out of the three remaining champions, I liked Steven the least, but as for who to heal...God, don't make me choose! Red was the first REAL challenge I had back when I first started Pokemon, so there's a lot of nostalgia. The first time I battled Cynthia on the other hand, I beat her pretty easily.
So, difficulty: RED
PERSONALITY
Cynthia has a much clearer and more colorful persona than Red, who is still a blank slate even as an NPC. No dialouge proves him to be the strong, silent type, but it doens't help his character very much. Cynthia on the other hand is helpful, and fascinated with Pokemon Mythology. She shows a great deal of caring for the Pokemon world, going to great lengths to try and support it. This is a very one-sided debate.
Personality: CYNTHIA
NOSTALGIA
As I said before, Red was the first ever true challenge I had when I started Pokemon with Heartgold version. When I made my way up to Mount Silver, I was certainly expecting a great challenge. Red surpassed that, and immediately kicked me back down to the bottom. That was the first time I had ever lost to an NPC. When I battled Cynthia years later, She was surprisingly easy, and I had known Red for much longer.
Nostalgia: RED
So, the final results are:
RED: 36 HP HEAL
STEVEN: 8 HP HURT
CYNTHIA: 51 HP