Well to me the best shinobi are the ones who do the best they can with what they have, strategize and plan, and have courage.
All three definitely have these traits, but to me Hinata takes it.
Its been made very clear that between a negative/neglecting father, cousin, and probable even sister she qd prêter much no one to encourage her. However, she would still continúe to practice even though it would never pay off.
But I'd say its her courage that makes her a real shinobi. Even though she is a gentle and somewhat pacifistic person she entered the exams with Kiba and Shino to improve as well as not let them down. When standing up against Neji, who clearly outclassed her...she actually managed to come close to landing a hit...pretty impressive for no natural fighting instincts as well as Neji's superior skill.
And standing up to Pain was ridiculous....I mean there were plenty of other people near Hyuga members who should have known he was down, but only Hinata went down to help. Considering the power difference and the fact she knew she was outclassed....damn crazy courage. I know love has a part to do with it, but honestly there's a limit to how much influence it can have.
Finally, with Neji's death. Neji didn't even have to die. Hinata was ready to die as a human shield. If that doesn't scream true shinobi I don't know what would. On top of that, with Neji's death, she had to be the one to snap Naruto back into action. It's her literal half brother who's dead, and yet she had to help someone else up

. Add in some of the lesser times she's helped Naruto emotionally (written test and before his fight with Neji), and she's got one of the requirements needed of a leader (morale boosting).
But like I said, the fact that Hinata may not be the strongest shinobi, bit het willingness to give her all no matter the adversary is admirable to me.
I don't think we need to discuss the important things Sakura has done (should be obvious....main character and all). And Ino isn't strong combat wise, but as a Sensor shinobi goes...she's basically the best one out there.
End of the day, they all fill their respective roles to the best of their ability, but from what I've already said and a pinch of bias, I give it to Hinata.