I can't choice anything because thats defends from the story. Is it a pairing I do love and the fic is captivating me than I want to read the whole fic in once. If that's just interesting I would choice "chaptered in irregular installmaents" if the fic can faszinate me. And if the fic is wonderful and great but not captivating because it's not my pairing or I don't know the show very well I would choice the first option.