Copy pasting my entry to the Second Annual Best Character Contest. Also I don't like calling a character waifu, but Hanekawa is definitely a best girl.
Hanekawa and the Tsubasa Chronicles
Hanekawa Tsubasa is hopelessly attractive. From her gorgeous face, her sexy back, her luscious breasts, and her curves; not to mention her seductive nature.
Hanekawa Tsubasa is intelligent; top of her grade, and is able to answer any queries and troubles from everyone.
Hanekawa Tsubasa is hopelessly kind. Selfless, fearless, she knows when to comfort and when to be defiant.
Why is she the best girl then?
Tears, fears, sears, and dears; we have followed her through every single step of her nightmares and cares, and we see her develop to the beauty of the best girl she became at the end of her story.
As we delve deeper into the series, we slowly uncovered layer upon layer upon layer of her identity.
In Kizumonogatari, she is attractive, she is intelligent, she is hopelessly kind, and she Kizumonogatari Spoilers
In Nekomonogatari: Kuro, she is attractive, she is intelligent, she is hopelessly kind, and she Nekomonogatari: Kuro Spoilers
In Bakemonogatari, she is attractive, she is intelligent, she is hopelessly kind, and she Bakemonogatari Spoilers
In Nekomonogatari Shiro, she is attractive, she is intelligent, she is hopelessly kind, and she Nekomonogatari: Shiro Spoilers
While other girls have unique traits or powers to be even memorable, Hanekawa Tsubasa is the Best Girl simply because we saw her Monogatari Series Spoilers.