Blaine was pretty cool. I loved the pokemon he had in his team and it was the most challenging gym i faced. I had no water-types and half my team had a weakness to fire.
RSE: Norman because of his incredible difficulty for a 5th Gym Leader. I honestly don't think I've ever beaten him without using Hyper Potions. Those Slakings are a pain in the ass.
FRLG: Koga because of his relentless use of status ailment inflicting moves. Nothing worse than being being poisoned with Toxic, and all four of his Pokemon have the move. That match has the potential to be frustrating if you don't have a trusty Psychic type on your team.
Wow, I picked the two 5th Gym Leaders. Purely coincidentally.