Most Helpful Girl
Maybe The Complete Tales and Poems of Edgar Allan Poe. Not only do I love it because it's Poe bt because I think it's this huge, hardback book that just looks ridiculously beautiful on the shelf:
Most Helpful Guy
I almost want to say Kansainvälinen Seikkailijan Opas now that you posted the picture of it, great book :D But I think I'll have to go with Malignant Self Love: Narcissism Revisited or And Then There Were None. I can never decide between those.