Ladies and gentlemen I give you the ever-hopeful, joyfully kind, and unfailingly loyal Luna Lovegood.
Despite being bullied and made fun of in school, Luna trusted the trio and the rest of the DA without question. She doesn't behave as if she ever expects them to be unkind to her, which is some kind of amazing. It is almost implied that Luna never had friends before Ginny, Neville, and the trio and yet she didn't even hesitate to join them on their rescue mission to the Ministry of Magic. Despite being shunned for her oddities in the past, it took a single branch of friendship from those five to inspire unshakeable loyalty. She never grew bitter or resentful, and never closed herself off from her peers. She lived hopefully for the day she would have a true friend and saw those hopes fulfilled.
As for being kind, who else but Luna could be trapped in a dungeon for months and still be courteous and helpful to others? She took care of Ollivander as best she could in a very terrible situation. He called her, "an inexpressible comfort...in that terrible place." When Harry, Ron, Dean, and Griphook arrived she reacted with neither agitation or despair. Just by the way she spoke, casually mentioning the nail they use when they need to break things being in proximity to the water jug (which was important because she was living in an environment in which they could not see), we can tell she made the best of the situation. She didn't even get upset with Ron when he was being difficult and instead spoke with "please" and "thank-yous."
Dobby's death was quite a blow to Harry, but Luna's suggestion that they close Dobby's eyes must have been healing for Harry's heart, giving the elf an appearance of peace and dignity no less deserved than Dumbledore himself. Remember it is she who spoke Dobby's eulogy with respect, saying all the words Harry could not.
As for loyalty, Luna never backed down. She stood with the DA against Umbridge and at the Battle of the Ministry. She stood against Death Eaters on the Astronomy Tower. She stood against the Carrows both before and after her stay at the Malfoy Manor. She stood until the end.
Luna is the most Hufflepuff Ravenclaw I've ever heard of, and I do believe that at the center of our hearts we should all have a little Hufflepuff inside.