Lemme put a word in for D.Va.Not only is she adorable, her Meka is one of the toughest things in the game, which gives you a lot of room for error. She can fly, fairly effectively, and she has a bullet shield ability too.
And, when she's actually firing, the pace of her game slows down to something more like Bastion-Lite, because she has to brace herself and that leaves her clomping around like a geriatric but that's okay, because she has the infinite ammo cheat up.
Really, the only thing I didn't like about her was that her guns are Computer Game Shotguns, so you have to climb right into somebody's face to use them.
Oh, and, for her ultimate - remember that, while your teammates are immune to the explosion, you are not. Therefore, run like a bunny.
-----
The most wonderful thing about BBs
Is BBs are wonderful things
Their sides are made out of iron
Their guns are made out of pain
They're crashy smashy bashy flashy fun-fun-fun-fun-fun
But the most wonderful thing about BBs
Is there is more than one
The~re is more than one!