My favorite was probably Elesa's second gym because I thought it would be cool to have your gym battle in front of so many people.
My type? Is that even a question with me? Grass, obviously.
I would like to be the sixth, or seventh, gym encountered in the game. My gym would be high up in the forest where you would have to swing from tree to tree using vines, using holes in the trees to get to new levels, and eventually work your way to me. Encountering trainers along the way. We need more grass type gyms anyway.
Team (since gym leaders don't normally have six pokemon):