Chapters and verses.
Not simply because chapter divisions break up a good story--none of the gospel writers wrote their work with embedded chapters. Each gospel was meant to be read (and heard!) as one, long story.
Neither because chapters and verses lead to misguided interpretations of Paul's letters. Romans is one, long argument. You can't take a verse or two from Romans, examine it, then stick it back in. Indeed, Paul builds argument upon argument in Romans like Jenga blocks. Pull the middle block out and the whole thing falls down. The only way you'll know what Romans 10:9-10 means is to read Romans 1:1-10:8 and 10:11-16:27.
Yes, context is crucial. Yes, chapters and verses imply it's not. But, that's not the most horrible thing about these man-made, artifical divisions.
Chapters and verses spawn "Bible References." And, why do we have Bible References? Well, they're often used to prove our answers to certain questions are "biblical." Now, they can serve as literary pointers to certain parts of Paul's argument or Luke's story. That can be helpful. But, that's not how we use them (either as writer or reader). Readers rarely "look up" the reference (my wife points this out all the time, either in her reading or when listening to Sunday School lessons). Because, if we looked up the reference, we might be led to say, "Hey. That's not what that means." Then, we'd all have to get our Bibles out, read the verse in context, which would take a lot of time that we don't have, and then we'd be left with the unsettling reality that most Bible References don't support the nice, clean, simple answers we need. Life is more complicated than that: relationships, work, money, jobs, help, society, culture--these things are very complex. So, most of us want at least one thing in our life that's not complicated: our faith. And, here's the really dangerous part, that's what most writers/speakers know. We don't want a faith that's hard to think about.
Enter Bible References. Confused about your relationships? Read this verse. Want to have a successful job? Read this verse. Want to feel better about your life, your world? Read this verse. Want to know why these people are wrong and we're right? Read this verse. Want to know what to believe about the most important decisions in your life? Read this verse.
"Who has time to read the whole thing? We should be grateful we have experts to point us to the important parts. Besides, who wants to read the parts that don't answer our questions?"