9. Squirrel Girl
The most interesting thing about Squirrel Girl, by all means, is her ability to be technically the most powerful superhero in the universe, if only entirely for comedic effect. Given her powers are supposed to only consist of super-strength and an ability to talk to squirrels, the punchline of Squirrel Girl is taking someone whose powers should be pretty much negligible, and making them overpowered anyway.
Squirrel Girl has defeated Thanos, Galactus, Doctor Doom, and pretty much any other insanely powerful character you could think of - and with ease, too. It serves to be effective on two levels - firstly, that it's refreshingly different and funny, and secondly, that it's hilarious seeing people absolutely lose their mind over her doing feats that are supposed to feel impossible, because that's the whole point.
Squirrel Girls plays on the ridiculous nature that all incredibly powered heroes possess, and that's exactly what makes her so engaging as a character - all potential side controversies aside.