Which a better books, hard cover or paper back?

i know it depends alot on the person, but i love to keep my books tidy and unmarked, i have found that the spine on a paper back book gets marked by the opening of books, is it worth that extra $10 a book to go hard cover or do they just fall apart like some rumours say?, i know several of my harry potter books which were hard cover fell apart but that is probally do to the strenuous use by my family of 5 and my sister who has no repect for her propety, my property or things everyone shares.... anyway, what is yuor opinion before i buy these books