The original champion from R/B/Y and FR/LG. It was the first champion I ever faced, and it was my hardest. I was literally down to my Zapdos and Charizard when I won, and both were at low HP with no chances of restoring health (I had used all my potions).
I think Blue, I disagree with Cynthia, just because she has a garchomp doesn't mean she should be hard or champion at all in my opinion.