Annie's the fourth ranked overall in her military graduating class, and is a Titan shifter, which could be used as a super move of some sort. She's an expert hand-to-hand combatant and excellent in 3D Maneuver Gear use, so you've got that to base her fighting style on, and a dash if you want that sort of thing.
Although I suppose that you could easily use Erin Yeager instead of her. The fighting style would be exactly the same, but I just like Annie's looks better (hoodies FTW), and of the top ten ranked graduating trainees (of which Erin is 5th overall), I kinda see her as the smartest of the bunch. But she's a villain, so that sucks.
So if you want Erin instead, here's a headshot of him:
(I know that you stated that you didn't want people putting in multiple suggestions, but in a sense, I'm kinda only doing one with two variants, which I leave to your preference.)