Hilda has a very bold and mature design. It makes her look the most competent out of all the female protags. If I were to pin it down, it's due to her ripped shorts that expresses a certain tone of a more mature sexiness that the other female protags lack IMO, coupled with her large boots conveying that she is ready to kick ass and travel the whole world. Topping it all off is her cap. The iconic signature standard to Pokemon Protag trainer cap, donned by Trainer Protags such a Red, Ethan, Hilbert, and Elio. Hilda is the ONLY female protag to wear a cap. That is a bold statement in of itself. And of course her amazing hair, even wearing her cap, you can tell she still takes a lot of care for her hair and grooming her self in general, even when dealing with the everyday responsibilities of being a Pokemon Trainer. Again, it's that mature sexiness that puts her above the rest.