I prefer to own books. I can never fully enjoy books I borrow, as a result of my slow reading. I get so needlessly time-conscious reading them to the point of ruining the experience. Beside, I like to have the books I've read at hand in case I have the sudden urge to go through them again. I even buy the borrowed books I've finished just to have them in my collection. On second thought, it might be less "collecting" and more "hoarding".