Kanto: Lorelei. Cool, suave, master of Ice types. She was a really fun character in the manga, too.
Johto: Karen, for her cheeky and confident spirit. Plus, she's the first Dark type user, which makes her unique.
Hoenn: Drake. Sea captain and dragon tamer, tempered and toughened by many a raging storm! Also that mustache.
Sinnoh: Eh, Flint. He's a funny hothead kind of guy. Most forgettable generation, I don't really like any of them tbh!
Unova: Caitlin. Elegant little princess that's tougher than she looks. Her design is one of my favorites, it's so delicate and feminine.
Kalos: Wikstrom, the knight in shining armor. Awesome steel types, love his character/design, plus he's a total babe <3.
Champions: Cynthia. She's really the only one that presented a challenge for me. Her team is by far the most balanced and interesting, and she is by far the most interesting in terms of relation to the story.