I think my favorite Gym Leader is pretty obvious. c':
My least favorite, however, is most definitely, and will always be, Skyla. I CAN'T STANDZ HER. She has this ISSUE of wanting to hurt the challenger really badly. Plus, her hair annoys me. A lot. Looks like a red pimple on her head that she tries to make less ugly by putting a little bow around it or something stupid like that.