Many cracking nominations here. But we can't have a waifu war without the people's favourite tsundere.
I am talking about of course, the endearing biri-biri from To Aru Majutsu no Index series, Misaka Mikoto.
In the anime world saturated with massively buxomy and voluptuous figures, Misaka's appearance and design is believable and realistic. She is slender, yet athletic. This does not allow her to be reduced to mere fanservice acts, which many fail to escape the clutches from. Delivering roundhouse kicks that Bruce Lee would be proud of, you can count on free ice cold beverage to quench your thirst in her company.
Misaka is not your run of the mill, damsel in distress. Far from it in fact. As a level 5 electromaster, she is arguably the strongest female character from her series. She is an adorable badass, being both cute, but extremely capable of kicking ass at the same time. Her power of electromagnestism allows her to whip up a lightning storm, attract and repel magnetic materials, creating weapons out of iron sand, to mundane day to day stuff like cooking, or even hacking computers.
But none of these are as exciting as her signature move, which Misaka earns her title of 'Railgun' from. She literally throws money at her target, with electromagntic propulsion.
Despite her strength, Misaka remains relatable to audience because she there are times when she is vulnerable. Which ties in to her character development. In the novels, she started off as a cocky character with a chip on her shoulder. Which is understandable as she is one of the most powerful espers in her city. As the story progresses, she eventually learn to accept what she can't accomplish on her own. She then accept help and support from others, and learn to trust more in her allies.
But perhaps more importantly, she possess the trait all great waifus should have - loyalty. She is always a pillar of support for Touma, often requests to help him, and reminding him he is not alone in fighting his battles. And she also does not have to rely on her love interest as a catalyst for her development. Which many heroines suffer from.
And of course, her classic moe expressions.
And she plays the violin.